IEC TS 63346-2-2:2026

• Abstract:

  IEC TS 63346-2-2:2026 provides common rules and specific requirements for the design of low voltage DC auxiliary power systems (APSs) intended to be installed in substations, mainly covering the configuration of DC power sources, system wiring, electric equipment selection and physical layout. For the purpose of interpreting this document, a DC APS in this document is considered as follows.; Its scope covers from the low voltage AC input of the charger to the DC input points of loads. Though DC load is discussed where necessary, the load itself is beyond the scope of this document.; Unless particularly stated, DC APS refers to the system using lead-acid and nickel-cadmium cells which are connected in series. The system using parallel cells can implement this document by reference.; Substations in this document refer to those which are part of an electrical system and contain equipment that either receives and distributes electrical energy or transforms voltages to the levels required by the loads they supply, or both.; This document does not apply to the design of any of the following: traction substation, which have different power supply requirements, such as unbalanced load power supply and harmonic behaviour;; offshore substations, as factors such as waves, typhoons, salt spray, etc. need to be taken into account, which have different requirements for power supply and equipment selection; the substation connecting a nuclear power plant to the grid and its associated LV APS integrated with the nuclear power plant.

• Status: Published
• Publication Date: 14-Jul-2026
• ICS: 29.240.01 - Power transmission and distribution networks in general
• ICS: 29.240.30 - Control equipment for electric power systems
• Technical Committee: PC 127 - Low-voltage auxiliary power systems for electric power stations and substations
• Drafting Committee: WG 3 - PC 127/WG 3
• Current Stage: PPUB - Publication issued
• Start Date: 15-Jul-2026
• Completion Date: 24-Jul-2026

IEC TS 63346-2-2 ®
Edition 1.0 2026-07
TECHNICAL
SPECIFICATION
Low-voltage auxiliary power systems -
Part 2-2: Design criteria - Low-voltage DC auxiliary power systems for
substations
ICS 29.240.01; 29.240.30 ISBN 978-2-8327-1377-8

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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms. 7
4 General requirements. 8
4.1 General . 8
4.1.1 System typical configuration . 8
4.1.2 Design principles . 8
4.2 Electrical requirements . 9
4.2.1 Design considerations . 9
4.2.2 System earthing . 10
4.2.3 System voltage . 10
4.2.4 Overvoltage protection and insulation coordination . 10
4.2.5 Requirements of AC source . 10
4.3 Safety requirements . 11
4.4 Environment requirements . 11
5 Load . 11
5.1 General requirements. 11
5.2 Load classification . 11
5.3 Load calculation . 12
6 System structure and wiring . 13
6.1 General requirements. 13
6.2 Typical structure of the main part . 13
6.2.1 Basic system . 13
6.2.2 System with two sets of batteries . 14
6.3 Distribution network . 15
6.3.1 General requirements . 15
6.3.2 Star network . 15
6.3.3 Meshed network . 17
7 Protection, monitoring and control . 18
7.1 General requirements. 18
7.2 System protection . 19
7.2.1 Configuration principle . 19
7.2.2 Selection of protective devices . 19
7.2.3 Protection selectivity and coordination . 20
7.3 Monitoring and control . 20
7.3.1 Configuration principles . 20
7.3.2 Data collection and alarms . 21
7.3.3 Main monitor . 21
7.3.4 Battery monitor . 21
7.3.5 IMD and IFLS . 22
8 Equipment selection . 22
8.1 General requirements. 22
8.2 Battery . 22
8.2.1 General requirements . 22
8.2.2 Battery size . 23
8.3 Charger . 24
8.3.1 General requirements . 24
8.3.2 Technical characteristics requirement . 25
8.4 Cable . 26
8.4.1 General requirements . 26
8.4.2 Electrical performance requirements . 26
8.5 Cabinet and distribution board . 27
8.5.1 General requirements . 27
8.5.2 Electrical performance requirements . 27
8.6 Battery discharge equipment . 28
8.6.1 General requirements . 28
8.6.2 Electrical performance requirements . 28
8.7 DC/DC converter . 29
8.7.1 General requirements . 29
8.7.2 Technical characteristics requirements . 29
8.8 Complete set of DC power supply . 29
8.8.1 General requirements . 29
8.8.2 Electrical performance requirements . 29
9 Equipment layout . 30
9.1 General requirements. 30
9.2 Battery layout requirements . 30
Annex A (informative) Demand factor for load statistics . 31
Annex B (informative) Signal information table . 32
Bibliography . 35

Figure 1 – Schematic diagram of a DC APS . 8
Figure 2 – Typical wiring diagram of single battery with single charger scheme . 13
Figure 3 – Typical wiring diagram of two batteries with two-charger scheme . 14
Figure 4 – Typical wiring diagram of two batteries with three chargers-scheme . 15
Figure 5 – Typical wiring diagram of star connection . 16
Figure 6 – Typical wiring diagram of star connection with sub-distribution boards . 17
Figure 7 – Typical wiring diagram of loop connection network . 18

Table 1 – Main parameters of the charger . 25
Table A.1 – Reference values of demand factor for load statistics . 31
Table B.1 – Signal information table . 32

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Low-voltage auxiliary power systems -
Part 2-2: Design criteria -
Low-voltage DC auxiliary power systems for substations

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
IEC TS 63346-2-2 has been prepared by IEC project committee 127: Low-voltage auxiliary
power systems for electric power stations and substations. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
127/86/DTS 127/89/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 63346 series, published under the general title Low-voltage auxiliary
power systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This part of IEC TS 63346 provides common rules and specific requirements for the design of
low voltage DC auxiliary power systems (APSs) intended to be installed in substations, mainly
covering the configuration of DC power sources, system wiring, electric equipment selection
and physical layout.
For the purpose of interpreting this document, a DC APS in this document is considered as
follows.
– Its scope covers from the low voltage AC input of the charger to the DC input points of loads.
Though DC load is discussed where necessary, the load itself is beyond the scope of this
document.
– Unless particularly stated, DC APS refers to the system using lead-acid and nickel-cadmium
cells which are connected in series. The system using parallel cells can implement this
document by reference.
Substations in this document refer to those which are part of an electrical system and contain
equipment that either receives and distributes electrical energy or transforms voltages to the
levels required by the loads they supply, or both.
This document does not apply to the design of any of the following:
– traction substation, which have different power supply requirements, such as unbalanced
load power supply and harmonic behaviour;
– offshore substations, as factors such as waves, typhoons, salt spray, etc. need to be taken
into account, which have different requirements for power supply and equipment selection;
– the substation connecting a nuclear power plant to the grid and its associated LV APS
integrated with the nuclear power plant.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60038, IEC standard voltages
IEC 60287 (all parts), Electric cables - Calculation of the current rating
IEC 60364-1, Low-voltage electrical installations - Part 1: Fundamental principles, assessment
of general characteristics, and definitions
IEC 60364-4-41, Low-voltage electrical installations - Part 4-41: Protection for safety -
Protection against electric shock
IEC 60364-4-42, Low-voltage electrical installations - Part 4-42: Protection for safety -
Protection against thermal effects
IEC 60364-4-43, Low-voltage electrical installations - Part 4-43: Protection for safety -
Protection against overcurrent
IEC 60364-4-44, Low-voltage electrical installations - Part 4-44: Protection for safety -
Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-51, Electrical installations of buildings - Part 5-51: Selection and erection of
electrical equipment - Common rules
IEC 60364-5-52, Low-voltage electrical installations - Part 5-52: Selection and erection of
electrical equipment - Wiring systems
IEC 60623, Secondary cells and batteries containing alkaline or other non-acid electrolytes -
Vented nickel-cadmium prismatic rechargeable single cells
IEC 60664-1:2020, Insulation coordination for equipment within low-voltage supply systems -
Part 1: Principles, requirements and tests
IEC 60896-11, Stationary lead-acid batteries - Part 11: Vented types - General requirements
and methods of tests
IEC 60896-22, Stationary lead-acid batteries - Part 22: Valve regulated types - Requirements
IEC 60898-3, Electrical accessories - Circuit-breakers for overcurrent protection for household
and similar installations - Part 3: Circuit-breakers for DC operation
IEC 60947-2, Low-voltage switchgear and controlgear - Part 2: Circuit-breakers
IEC 61056-1, General purpose lead-acid batteries (valve-regulated types) - Part 1: General
requirements, functional characteristics - Methods of test
IEC 61439-1:2020, Low-voltage switchgear and controlgear assemblies - Part 1: General rules
IEC 61439-2, Low-voltage switchgear and controlgear assemblies - Part 2: Power switchgear
and controlgear assemblies
IEC TR 62060:2001, Secondary cells and batteries - Monitoring of lead acid stationary
batteries - User guide
IEC 62259, Secondary cells and batteries containing alkaline or other non-acid electrolytes -
Nickel-cadmium prismatic secondary single cells with partial gas recombination
IEC 62485-2, Safety requirements for secondary batteries and battery installations - Part 2:
Stationary batteries
IEC TS 63346-1-1, Low-voltage auxiliary power systems - Part 1-1: Terminology
IEC 63346-2-1, Low-voltage auxiliary power systems - Part 2-1: Design criteria - General
requirements
___________
Under preparation. Stage at the time of publication: IEC TS/BPUB 63346-2-1:2025.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purpose of this document, the terms and definitions given in IEC TS 63346-1-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
capacity
electric charge which a cell or battery can deliver under specified
discharge conditions
Note 1 to entry: The SI unit for electric charge is the coulomb (1 C = 1 A·s) but in practice, capacity is usually
expressed in ampere hours (A·h).
[SOURCE: IEC 60050-482:2020, 482-03-14]
3.1.2
ambient temperature
temperature of the air or other medium within the proximity of an
electrical installation
[SOURCE: IEC 60050-826:2022, 826-10-03]
3.1.3
isolated system
IT-system
system in which no live part is intentionally earthed, except for high impedance connections for
protection or measurement purposes
[SOURCE: IEC 60050-195:2021, 195-04-07, modified - The second term "IT-system" has been
added.]
3.1.4
meshed network
arrangement of electric conductor and boards forming a combination of star and loop circuits
3.2 Abbreviated terms
AC alternating current
APS auxiliary power system
CB circuit breaker
DC direct current
HV high voltage
IFLS insulation fault location system
IMD insulation monitoring device
IT isolated terra
LV low voltage
Ni-Cd nickel-cadmium
PCE power charger equipment
PE polyethylene
PVC polyvinyl chloride
UPS uninterruptible power system
VRLA valve regulated lead-acid battery
4 General requirements
4.1 General
4.1.1 System typical configuration
A DC APS typically consists of a battery, charger, distribution network, monitoring equipment
and control devices as shown in Figure 1.

Key
PCE power charger equipment
Figure 1 – Schematic diagram of a DC APS
During normal operation, chargers convert AC to DC to supply DC loads and maintain the
battery on float charge. In case of AC system failure, the battery remains connected to the DC
bus, supplying loads for a specified duration until AC power is restored.
This document delineates the DC APS into two segments: the main section from the AC input
of the charger to the DC bus, and the distribution network from the DC bus to the load, with
details outlined in Clause 6.
4.1.2 Design principles
This document identifies DC APS with different classes of reliability requirements by
considering aspects such as adequacy, redundancy and safety from which the station owners,
designers and other interested parties can select their best-practice system.
The following principles should be followed in the design of a DC APS.
a) A comprehensive consideration of economy, reliability, flexibility and safety based on a
thorough understanding of the specific requirements of project construction, system
operation and maintenance.
b) The determination of the system capacity, the selection of the system voltage, the system
structure, the protection configuration, the selection and arrangement of the equipment,
etc., which should all be based on the characteristics of the primary system. The DC APS
design should avoid the common point of failure which can lead to a total power outage of
the substation.
c) Fulfillment of quality of supply requirements.
d) Determination of battery autonomy or standby time based on specific circumstance.
NOTE The substation can be subject to standards and regulations in the country where it is located.
The factors that influence the determination of battery autonomy or standby time include the
following.
– The importance of the site or equipment from a network management perspective.
– The position of the site on the network re-energisation time schedule. Sites that are closer
to the black start origin will be re-energised earlier than sites that are located further away.
– The distance of the site from the nearest technical service centre.
– The accessibility of the site. Sites that are close to national highways and have normal road
access are easier and faster to reach compared to sites that are in rural areas, where an
off-road vehicle is required or access is necessary.
– The availability of spares. Is it readily available or needs to be sourced from a central
location that could take several hours.
– The accessibility of the site to the electricity network (grid-connected). Sites that are not
connected to the grid and rely on renewable energy sources (wind or solar) require much
longer standby times due to the variability of the energy source.
– The reliability, capacity, availability and flexibility of the AC input power sources, for
example, diesel generators.
If the substation has a load centre (for example, series compensation equipment area,
controllable high-resistance reactor area, SVG area), and this area is located far from the other
DC loads making it difficult to meet cable voltage drop requirements, a separate dedicated DC
APS may be set up.
Electric power supply for telecommunication systems in the substation shall be considered
when designing DC APS. The power supply system for telecommunication systems may be
configured independently or integrated with the DC APS in the substation, depending on the
importance of the substation.
If integrated with the DC APS, one or more independent DC/DC converters may be configured
to supply power to the telecommunication systems.
4.2 Electrical requirements
4.2.1 Design considerations
The system structure of a DC APS can vary depending on the specific substations, which is
discussed in Clause 6. When selecting a system structure, it is important to consider the
following aspects:
– operating scenarios;
– redundancy requirements;
– protection philosophies;
– reliability requirements;
– system flexibility requirements;
– electrical filtering requirements;
– physical distance between DC loads and DC APS.
4.2.2 System earthing
The system earthing of DC APS shall comply with IEC 60364-1.
For the continuity of supply, a DC APS shall be designed as an isolated system, also known as
a DC IT-system. The main characteristics of an isolated system include the following:
– The output of the system is electrically separated from the AC input.
– The output of the system is electrically separated from the frames and shells of the
equipment.
– There is no intentional grounding of any live parts of the system, except for
high impedance connections used for measurement purposes.
– Circuit disconnection is not required during single fault conditions.
NOTE The requirements for IT systems are specified in IEC 60364-4-41.
4.2.3 System voltage
The nominal voltage and the maximum operating voltage of the system shall be agreed upon
by the users and manufacturers.
The choice of nominal voltage shall consider the following factors:
– legacy systems or relevant industry requirements;
– load profile and distribution area;
– local standard design practices.
NOTE Local regulations can apply.
The typical nominal voltages for DC APSs in substations shall comply with IEC 60038 mainly
including 220 V and 110 V.
The operating voltage of the DC APS depends on the load and battery operating voltage
windows.
The minimum system voltage shall meet the minimum operating voltage requirements of the
connected loads.
4.2.4 Overvoltage protection and insulation coordination
The insulation coordination of the system shall be designed in accordance with
IEC 60664-1:2020. The selection of electric insulation technical characteristics for APS
equipment shall be based on its applications, surroundings and environmental conditions.
Clearances shall be dimensioned in compliance with IEC 60664-1:2020, 5.2.
Creepage shall be dimensioned in compliance with IEC 60664-1:2020, 5.3.
Solid insulation shall be designed in compliance with IEC 60664-1:2020, 5.4.
4.2.5 Requirements of AC source
To reduce the risk of power loss in the DC APS, two independent AC input power sources can
be provided for the charger. The two AC input power sources can be switched manually or
automatically.
Equipment shall be selected with suitable power characteristics for normal operational
conditions. For DC APS, the voltage fluctuation range should not exceed –15 % to +20 % of the
nominal voltage (RMS value for AC).
The rated frequency of the equipment shall correspond to the frequency of the current in the
circuit. If the frequency has an impact on the characteristics of the rectifier, the power quality
should meet the requirements of the manufacturers.
4.3 Safety requirements
The requirements for protection against electric shock, thermal effects, overcurrent as well as
voltage disturbances and electromagnetic disturbances in LV electrical installations specified
in IEC 60364-4-41, IEC 60364-4-42, IEC 60364-4-43, and IEC 60364-4-44 shall apply.
Reference should be made to this document as applicable in the DC APS.
Measures for protection against hazards generated by batteries shall be ensured in accordance
with IEC 62485-2.
4.4 Environment requirements
The environment requirements of the DC APS shall be in accordance with IEC 63346-2-1 .
5 Load
5.1 General requirements
The rated power and energy requirements of the DC APS are determined by the connected
loads and their associated load profiles. Information on all DC loads, including energy demands,
typical properties, and functions, should be gathered to design a DC APS with sufficient capacity
to supply these loads under normal and emergency conditions, ensuring continuous substation
operation during emergencies.
Given the diverse nature of loads, a statistical approach shall be taken to provide a rational
solution for the energy requirements.
5.2 Load classification
To calculate their capacity, DC loads shall be classified based on their operating characteristics
and nature, typically including the following.
– Continuous loads (or standing loads)
This kind of loads requires power supply in both normal condition and emergency cases.
EXAMPLE DC lighting, telecontrol, telecommunications, and protection relays.
– Emergency loads (or time-limited loads)
This kind of loads is powered only during the failure period of AC APSs.
EXAMPLE Emergency lighting, AC UPS.
– Momentary loads (or random loads)
Similar to continuous loads but requiring power for very short duration.
EXAMPLE Circuit breaker trip coil.
___________
Under preparation. Stage at the time of publication: IEC TS/BPUB 63346-2-1:2025.
According to the load function, they can be further grouped into control loads and power loads.
– Power loads
This kind of loads typically requires higher current ratings, resulting in bulkier installations
and larger voltage fluctuations as loads turn on and off.
EXAMPLE Auxiliary motors, circuit breakers, UPS devices, DC/DC converters, and emergency lighting.
– Control loads
This kind of loads typically has low power consumption but are sensitive to voltage
fluctuations.
EXAMPLE Instrumentation, automatic control devices, and relay monitoring equipment.
5.3 Load calculation
In order to design a reliable DC APS in a substation, the DC loads shall be identified and
quantified. The designer shall consider the ultimate plan for the substation in order to account
for anticipated future DC loads. After identifying the DC loads, demand factors and load factors
for each load should be applied. These factors aid in economically and reasonably sizing the
DC system and battery capacity.
The demand factor represents the ratio of maximum coincident demand of a system (or part of
a system) to the total load connected to the system (or part of the system), which can be
established for subsets of similar equipment (such as DC distribution board). The load factor is
the ratio of average load over a designated period to peak load occurring in that period.
For the DC APS with a single set of battery, the load capacity should cover both control load
and power load of the system, which means that the battery is capable to supply the entire
system.
For the DC APS with two sets of batteries, the load capacity supplied by each battery set should
be calculated according to the principles below.
– For DC APSs dedicated to control loads, each battery set should cover the total system
loads.
– For DC APSs supplying both control loads and power loads, each battery set should cover
total control loads plus half of the total power loads, which means that each battery set is
sized to supply all the control loads and half of the power loads of the system.
– When two DC APSs are connected via a tie breaker, the load of each APS should be
assessed independently, which means that the load capacity of the APS should not be
increased due to the possible power supply to the other APS.
– The anticipated AC power outage time or battery backup time should be determined by
relevant standards and regulations.
– The anticipated lifespan degradation of the batteries should be factored into battery capacity
design and also considering operating temperature.
In the absence of load information, refer to Annex A for demand factor and load factor in DC
load statistics.
6 System structure and wiring
6.1 General requirements
The structure of a DC APS system defines the operational philosophy, balancing factors like
economy, reliability, flexibility, and security. The following aspects shall be considered in
system structure design:
– operating scenarios, for example, manned or unattended substations;
– protection logic of the electric power system, for example, dual or single protection;
– importance of the substation, for example, substation scale, system voltage, and power
level;
– DC loads in the substation;
– relevant standards and regulations of the country or region;
– technological development level in the country or region;
– integration of DC APS, UPS, DC/DC converter and other devices.
6.2 Typical structure of the main part
6.2.1 Basic system
For a basic DC APS, the following requirements shall be met:
– for a configuration with one power supply (charger), one DC bus shall be used;
– a second power supply (charger) may be installed.
The basic configuration of a DC APS, as shown in Figure 2, consists of one charger and one
battery, which has the lowest redundancy, flexibility and reliability. Therefore, this configuration
should only be used in situations where the loss of the DC APS does not cause a significant
influence on the normal operation of electric power transmission system or power distribution
network.
Figure 2 – Typical wiring diagram of single battery with single charger scheme
The reliability can be increased by either additional power supplies, additional batteries or
additional of both devices (see 6.2.2). The specific number of additional chargers and batteries
needed will depend on the requirements of the power system and the desired level of reliability.
6.2.2 System with two sets of batteries
For substations with duplicate protection schemes, two batteries with a two charger-
arrangement, as shown in Figure 3, should be used so as to provide independent power to each
set of protective systems in the substation.

Figure 3 – Typical wiring diagram of two batteries with two-charger scheme
In this arrangement, each battery shall be able to power all DC loads in the substation. By
having multiple batteries and chargers, the system is more reliable and less susceptible to
failures. The redundancy of this arrangement allows for offline maintenance and replacements
to be easily performed, as well as the ability to quickly restore power after a fault occurs.
NOTE A scheme with reduced capacity can be installed to reduce initial cost. However, it is possible the financial
benefits do not justify the additional risk.
The following requirements shall be met.
– Sectionalized single-bus configuration is adopted.
– The two bus sections are electrically connected via an isolator or a tie circuit breaker which
is normally switched off.
– The two batteries do not run in parallel.
– Two or more chargers can be installed accordingly.
For substations with significant consequences from a blackout, a DC APS of higher reliability
as shown in Figure 4 should be considered. The additional charger scheme provides greater
reliability and capacity at the cost of increased complexity and lower economic efficiency. It
involves installing and maintaining additional devices, leading to higher operational costs and
potential technical challenges. Despite these drawbacks, the additional charger scheme
provides improved system reliability and flexibility, and can reduce the risk of charger downtime.
Figure 4 – Typical wiring diagram of two batteries with three chargers-scheme
6.3 Distribution network
6.3.1 General requirements
The distribution network of an APS influences how equipment is connected, how it can be
isolated for maintenance and how it will isolate following a fault. The following aspects shall be
taken into account in the design of distribution networks:
– bus configurations, for example, single bus, sectionalized bus, or duplicated bus;
– network arrangements, for example, star connection, open mesh, or closed mesh;
– duplication and redundancy requirements, for example, single supply circuit, duplicated
supply circuit.
Two network arrangements are commonly used including star network (radial network) specified
in 6.3.2 and meshed network (loop network) specified in 6.3.3.
6.3.2 Star network
The star network shall be installed to supply loads requiring independent power supply, such
as relay and control loads.
The main characteristics of a star network is that the power is supplied to a load in a manner
that the circuit goes directly from point A to point B with no alternative supply available. Point
A can be the bus of a distribution board (or sub-distribution board) while point B is a load or a
bus of the sub-distribution board. The benefits of applying a star network include the following:
a) faults on one circuit will not affect other circuits;
b) it is easier to achieve protection coordination between protective devices.
A typical scheme is shown in Figure 5.

Figure 5 – Typical wiring diagram of star connection
Loads which require higher reliability or are of large capacities should be supplied by distribution
boards directly instead of sub-distribution boards, such as DC emergency lighting, UPS and
DC/DC converters.
Sub-distribution boards shall be applied serving the purpose of the following:
– simplifying the overall system wiring;
– saving the number of inlet and outlet cables;
– being closer to load centres, which can be relatively far away from distribution boards.
To increase power supply reliability of the sub-distribution boards, each bus section in the sub-
distribution boards should be fed by dual incoming lines. A typical scheme is shown in Figure 6.
Figure 6 – Typical wiring diagram of star connection with sub-distribution boards
6.3.3 Meshed network
Meshed network has alternative supply paths for fault tolerance so that if one path is lost,
another path can be used. The following characteristics should be considered when applying
meshed network:
– requiring isolating multiple sources under normal conditions and operated in parallel briefly
during switching;
– faults on one circuit can affect other circuits, complicating ground fault detection.
Meshed networks shall normally run open for independent power supply but can be closed
during maintenance or fault restoration period to maintain power supply to loads.
A meshed network should have at least two power sources with one serve as the main power
supply and the other serves as the standby power supply. A typical scheme is shown in Figure 7.
For example, to ensure the continuous power supply to the load during the power switch,
manually close CB5, where the two sets of batteries are temporarily paralleled, and then
disconnect CB3 or CB4 as soon as possible to complete the power switch.
If the two power sources of a meshed network from two independent batteries, manual power
transfer between the two sources should be used.
Figure 7 – Typical wiring diagram of loop connection network
7 Protection, monitoring and control
7.1 General requirements
Protection, monitoring and control devices shall be implemented in the DC APS to enable self-
supervision and fault identification and clearance, which helps to reduce the likelihood of latent
problems and periodic maintenance and inspection costs.
The configuration of protection, monitoring, and control functions shall be determined by
designers based on practical engineering requirements, including but not limited to the following:
– APS system structure;
– system parameters;
– equipment parameter;
– operation mode and reliability requirements.
The protection schemes as well as monitoring a
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