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IEEE1818 - 2017 Guide for the Design of Low Voltage AC and DC Auxiliary

Systems for SubstationsSponsored by the IEEE Substations Committee

Presented By Joe Gravelle

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Organization of the Guide1. Scope / Purpose2. Normative References3. Definitions4. AC System Design5. DC System DesignAnnex A – BibliographyAnnex B - Conductor Sizing examplesAnnex C – Battery Sizing Examples

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Organization of the Guide1. Scope / Purpose2. Normative References3. Definitions4. AC System Design5. DC System DesignAnnex A – BibliographyAnnex B - Conductor Sizing examplesAnnex C – Battery Sizing Examples

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1.1 Scope• This guide provides guidelines for the design of

the ac and dc systems. • This guide covers the low voltage auxiliary

systems from the source(s) to the distribution point(s).

• Reliability requirements and load characteristics

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1.2 Purpose• The low-voltage ac and dc auxiliary systems comprise

very important parts of the substation equipment. • Design of the ac and dc auxiliary systems

• reliability, • load requirements, • system configuration, • personnel safety, • safe and reliable operation• protection

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2.0 Normative References• IEEE 485, IEEE 525

3.0 Definitions• Definitions are provided for technical terms used

in the guide.

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Organization of the Guide1. Scope / Purpose2. Normative References3. Definitions4. AC System Design5. DC System DesignAnnex A – BibliographyAnnex B - AC examplesAnnex C – DC Examples

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4.0 AC System Design • Design Criteria• Source Requirements• Load Analysis• Conductor Selection• Transformer(s)• Transfer Switch • Bus Layout• Panels• Protection• Equipment Specifications• Operations and Maintenance

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4.1 Introduction• Design Criteria• Source Requirements

• Number of sources• 1 phase or 3 phase• Load Requirements

These sections define the AC system for the substation Application.

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4.2 Design Criteria • AC system loads• 1 or 3 phase• System stability• Protection• Voltage

This section defines the AC system design.

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4.3 AC sources • Transformer tertiary

• Substation bus

• Distribution line

• Generators

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4.4 AC Load Analysis • Identification

• Amps/Volts/kW

• Equipment rating

• Demand factors

• Load calculations

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4.5 Conductor Selection• Conductor Type

• Insulation

• Temperature Rating

• Size – Ampacity

• Voltage Drop

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4.6 Station Auxiliary Transformer • Transformer Type

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4.6 Station Auxiliary Transformer • Number of transformers

• Single/Three phase

• Transformer Ratings

• Transformer Connections

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4.6 Station Auxiliary Transformer • Transformer Ratings

• KVA• Voltage• Short Circuit • Impedance• BIL

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4.6 AC System Design • Transformer Connections Single Phase

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4.6 AC System Design • Transformer Connections Three Phase

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4.7 Transfer Switch • Manual / Automatic

• Considerations:

• Break before Make

• Switching Neutrals

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4.8 Bus Layout - Distribution Configuration• Essential / Non-Essential Loads

• Simple Radial System

• Expanded Radial System

• Primary / Secondary Selective systems

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4.8 Bus Layout and Distribution Circuit Configuration

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4.9 AC Distribution Panelboards

• Application• Ratings• Short Circuit ratings• Standards

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4.10 AC Auxiliary System Protection • Panelboard or Switchboard

• Circuit Breaker Selection

• Fuse Selection

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4.11 Equipment Specifications• General considerations

• Standards

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4.12 Operation - Maintenance Consideration• Accessible Disconnects

• Indoor/Outdoor Design

• Adequate Working Space

• Standby or Backup AC System

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Organization of the Guide1. Scope / Purpose2. Normative References3. Definitions4. AC System Design5. DC System DesignAnnex A – BibliographyAnnex B - AC examplesAnnex C – DC Examples

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DC System Design • Design Criteria• DC Equipment • One Line Diagram• Batteries• Chargers• Panels• Design Considerations • Maintenance Provisions

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Battery System

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Battery SystemSingle cell battery with acid

containment on a two step rack

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5.1 DC System Design Criteria • Reliability

• Redundancy

• Environment

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5.2 Equipment Served by the DC System • System Protection Equipment• Motor Operators• Breakers• SCADA• Fire Protection• Security

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5.3 One Line Diagram • Power System One Line

• System protection• DC System One Line

• DC Load Calculations• DC Connections• Number of Batteries• Load Transfer

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Substation One LineOperating sequence:

12D3 is normally closed, no generation on feeder circuitsOperating time for MOS 10 seconds

Transformer T1 differential:Trip 69CB1, 69CB3, 12CB1Open 69DT1

Breaker Failure on 12CB1:Open 12CB2, Open 12D3, Reclose 12CB2

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DC System

Battery

Battery Charger

Panel

To DC Cab.

Maint Charger & Battery

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DC System distribution cabinet(s)

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5.4 DC Batteries Battery System

Battery Charger(s)

Battery Disconnect(s)

DC Panel(s)

Maintenance Connections

DC Loads

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5.4 DC Batteries

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5.4 DC Battery Types Vented Lead Acid (VLA)

Valve Regulated Lead Acid (VRLA)

Nickel Cadmium (NiCad)

• For substation use, vented lead-acid cells are the most common

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5.4 DC Battery

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5.4 DC Battery

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5.4 DC Battery

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Battery SizingSizing the battery using IEEE 485 (Vented Lead Acid Batteries)

Defining the Duty Cycle (loading on battery based on time duration)

Continuous Load

Momentary Load

Worst Case Tripping

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Continuous LoadsIndicating lamps, Microprocessor Relays, Electronic Meters, SCADA Systems, Annunciators, Communication Equipment

o For loads that are non-linear such as power supplies, the current increases as voltage declines.

o The watt rating is typically used to determine current at end of battery cycle discharge voltage

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Momentary LoadsLock Out Relay (LOR) Breaker trippingMotor Operators Breaker Fail operation Considerations:

o Worst Case Tripping Scenarios

o MOD use Locked Rotor rating

o Breaker Fail use SOE not sum of all currents select highest

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Worst Case Tripping Operating sequence:12D3 is normally closed, no generation on feeder circuitsOperating time for MOS 10 seconds

Transformer T1 differential:Trip 69CB1, 69CB3, 12CB1Open 69DT1

Breaker Failure on 12CB1:Open 12CB2, Open 12D3, Reclose 12CB2

Timing:T=0cy (0 sec)Trip 69CB1, 69CB3, 12CB1, open 69DT1Current=12+12+8+60=92A

T=12cy (0.2sec) (12CB1 breaker failure timer)Trip 12CB2, Re-Trip 12CB1 open 12D3Current=20+8+8+60=96A

T=600cy (10sec)Reclose 12CB2Current=6A

From the above, the worst case tripping load is 96A for the 12CB1 breaker failure.

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Duty Cycle Duration1. Charger fails – Initiates Alarm to SCADA2. Dispatcher notices Alarm3. Dispatch contacts Substation Personal4. Substation Personal Drive to Substation5. Investigate Alarm6. Determines Charger Failed – contacts dispatch requesting maintenance 7. Dispatch contacts Maintenance8. Maintenance Technician Drives to Substation9. Maintenance attempts to repair charger (unsuccessful)10.Maintenance Supervisor locates spare charger11.Maintenance Supervisor contacts additional resources12.Resources drive to service center PU spare charger and drive to substation13.Replace failed Charger

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Duty Cycle Example

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Battery Chargers

Sizing battery Chargers

Charger Connections

Charger Circuit Protection

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Battery Chargers

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Battery Charger size

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DC Panels

Considerations

Critical Loads vs non-Critical Loads

Circuit size

Number of circuits

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DC Panels

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DC Panels

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Design Considerations• Battery location

• Maintenance considerations • Working clearances• Method for removing

battery cells• An eyewash station • Spill containment

systems• Terminal Covers

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Battery Terminal Covers

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Design Considerations

• Battery area temperature• Specifications published for sizing

• Heat and Cold impact battery performance

• Reference IEEE485 for effect on Battery Size

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Design Considerations• Acid spill containment

• Spill Pans• Acid-resistant paint on the floor

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Design Considerations• Battery racks

• Three types—step, tier, or stepped tier

• Height variations between cells can cause cell temperature differences within the same battery system

• acid-resistant coating applied to the structural frame

• seismic zone

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Design Considerations • Battery rack

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Design Considerations Circuit considerations • Grounded and ungrounded systems

• Ungrounded –Substation Control - SCADA

• Grounded ((+) grounded) – Communications

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Design Considerations -Circuit considerations

• Isolation of Main DC cables • Recommendations - IEEE 1375

• Battery fuse • Battery circuit breaker• Battery disconnect switch • Mid-point battery fuse

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Circuit considerations • Isolation of main dc cables - Separate the pos and neg cables

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Design ConsiderationsCircuit considerations

• Coordination of overcurrent protection• Short-circuit levels• Fuses• Breakers• Equipment voltage ratings

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Maintenance Provisions• Isolation switches

• Equipment accessibility

• Back-up supplies

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Maintenance Provisions• Testing Provisions

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DC System

Battery

Battery Charger

Panel

To DC Cab.

Maint Charger & Battery

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AnnexAnnex A – Bibliography

Annex B - Conductor Sizing Example

Annex C – Battery Sizing Example

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Questions?