Circuit Breakers and Switchgear - Thomas Greer

Circuit Breakers and
Switchgear

Thomas Greer
Director of Engineering
TLG Services

Presentation Outline

Switchgear Definition

Overcurrent Protection Devices

Circuit Breaker Trip Curves and
Coordination

Panelboard

Switchboard

Switchgear

Maintenance Bypass Configurations and
Applications

What is Switchgear?

IEEE defines switchgear as:

A general term covering switching and interrupting devices and
their combination with associated control, instruments, metering,
protective, and regulating devices; also assemblies of these
devices with associated interconnections, accessories, and
supporting structures used primarily in connection with the
generation, transmission and conversion of electric power.

The primary functions of UPS switchgear is:

– Circuit switching

– Short-circuit protection

– Over-current protection

Switching and Overcurrent Protection
Devices

Types

– Switches
• Disconnect Only - No Overcurrent Protection

– Fuses
• Cheap / Easy Replacement ☺
• Successful Operation = Destruction

– Circuit Breakers
• More Expensive Than Fuses
• Designed for Repeated Operation ☺

Circuit Breakers

Circuit Breakers

Basic Types

– Molded-Case / Insulated Case Circuit Breakers
• UL489 (for Switchboards and Panelboards)
• 80% rated - Molded Case – Typically Rated up to 1200A
• 100% rated – Insulated Case - Rated 800-4000A

– Low Voltage Power Circuit Breakers- LVPCB
• UL1066 (for Metal Clad Switchgear)
• 100% Rated

Molded Case Circuit Breakers

Fixed Mounted
Toggle Open-Close Operation

Molded Case Circuit Breakers

Features

– Ampere Ratings Typically 3A - 1200A
– Typically 80% Rated

• Continuous Current Not To Exceed 80% Of Nameplate

– Usually Fixed Mounted
– Toggle Handle for Manual Operation
– Thermal Magnetic Fixed Trip Most Common
– Magnetic Instantaneous Trip
– Designed for Quick Interruption / Limited Withstand Duration
– Minimal Maintenance Capabilities

Insulated Case Circuit Breakers

Drawout PowerBreak II

Easy Inspection and Maintenance of Primary Contact
Finger Assembly on Drawout Breakers

Insulated Case Circuit Breakers

Features

– Tested and Listed to UL 489
– Ampere Ratings up to 4000A
– Can be either Drawout or Stationary
– Two Step Stored Energy Mechanism

• Can be electrically operated

– Solid State Trip Units Most Common
– Low to No Maintenance

• Usually rated for 10,000 Operations

Low Voltage Power Circuit Breakers

GE WavePro LVPCB SqD Masterpact
NW and NT LVPCB

Low Voltage Power Circuit Breakers

LVPCB (aka - Iron Frame Breaker or Air Breaker)

– Tested and listed to UL1066
– Available in sizes up to 5000A
– Insulated Case Type or Traditional Iron Frame Construction
– Old Style Iron Frame Requires Maintenance and can be Rebuilt

• Inspection every 100 to 200 Operations
• Replacement of Contacts every 300 to 1000 Operations
– Newer Style Enclosed Have Maintainable Arc Chutes and Contacts
– Two Step Stored Energy Mechanism
– Trip units are typically electronic with selectable time current curve
characteristics
– Higher Short Time Ratings

Available Trip Units for Circuit Breakers

Thermal Magnetic

• Long-Time Overload Trip
• Bi-Metallic Strip

Magnetic Instantaneous

• Solenoid Response to High Current Setting
• Self-Protection Feature

Ground Fault Interrupt

• Current Summing CT

Solid State

• Long Time Setting / Delay
• Short Time Setting / Delay
• Instantaneous Setting / Delay
• Ground Fault Setting / Delay

Why The Different Types??

Various Breaker And Trip Types Designed For Optimum
User Flexibility In Designing The Power Distribution
System. The Secret To Success In Designing Power
Distribution Is,….

Coordination...

• Coordination...

»COORDINATION!!!!!

Selective Coordination

Selective coordination is the process of localizing a
fault to the overcurrent device closest to the fault.

Branch X
Device Fault
Opens

Reading a Trip Curve Header

Graphic representation Time in Seconds
– Tripping time

vs.
– Current level
– Shaded area -- possible trip

• Manufacturing tolerances

Multiples of 100
Rated Current

Thermal Tripping Thermal

Bi-metallic element responds to heat Time in Seconds
generated by the overcurrent
Shown in the upper left portion of the trip
curve
Overload currents (1X to 6X)
Inverse time - larger overcurrent opens the
circuit breaker faster

Multiples of Rated Current

Instantaneous (Magnetic) Tripping

Magnetic assembly responds to the Time in Seconds
current flow through the circuit breaker

Shown in lower right portion of trip curve

High level overcurrents (5x - 10x handle
rating or higher)

Trips instantaneously -
no intentional time delay

Magnetic

Multiples of Rated Current

Electronic Tripping

Utilizes a trip solenoid Long-time Pickup
Long-time Delay
Different tripping
characteristics achieved by Time in Seconds Short-time
adjustment of trip unit Pickup
functions
Short-time
I2T OUT Delay (I2T IN)

Instantaneous

Multiples of Rated Current

Trip Unit

PE Circuit breaker LSIG
1200 and 1600 ampere Sensor

Square D MICROLOGIC Trip Units

Standard Ampmeter Power Harmonic

Trip Unit Trip Unit (A) Trip Unit (P) Trip Unit (H)
LI, LSI LI, LSI, and LSIG LSI, LSIG/A LSI, LSIG/A

Where Are The Breakers Housed?

Panelboards
Switchboards
Switchgear

Panelboards

Front Cover Removed

Panelboards

According to the NEC (NFPA 70), panel boards are:
Used to control light, heat, or power circuits
Placed in a cabinet or cutout box
Mounted in or against a wall
Accessible only from the front

Switchboards

W/ FIXED MOLDED CASE BREAKERS W/ DRAW-OUT ICCB CIRCUIT
BREAKERS–REAR CONNECT’D

Switchboard Construction

UL 891 - Switchboard

– Referenced Standards:
• Enclosure: UL 891, NEMA PB-2

– Stand-Alone Enclosure Design
– Available in front access only or front and rear access
– Construction with internal barriers between devices and bussing

or control circuit is optional
– Can Utilize Molded Case, Insulated Case, and LVPCB’s
– Fixed-Mounted / Plug-In / Draw-Out Device Options
– Front Accessible for Fixed Mounted / Plug-In Devices

Switchgear

Typical UPS Integral Switchgear Lineup

Switchgear Construction

UL 1558 - Switchgear

– Referenced Standards:
• Enclosure: ANSI C37.20.1, UL 1558, NEMA SG5
• Circuit Breakers: ANSI C37.13, UL1066

– Stand-Alone Enclosure Design
– Generally Higher Amperage
– Low Voltage Power Circuit Breakers Only
– Rear access always required for installation and service
– Bus Bar Runbacks
– Breakers fully compartmentalized with barriers

Switchgear vs. Switchboard

Selection of switchgear or switchboard is a function of the
following:

– Application type:
• Switchgear used mostly for service entrance / substation
• Switchboard used mostly for load distribution, close to load

– Switchboard:
• More prevalent in lower amperage
• Lower short circuit current availability
• Load distribution / maintenance bypass applications

– Switchgear:
• Typically more costly
• Rear access requirement

Basic Switchgear Configurations & Uses

• Maintenance Bypass
• Load Distribution
• Power-Tie
• Integral System Control and STS

Maintenance Bypass
Configurations

What is a Maintenance Bypass??

Intended to be a path for power to the critical load, wrapping around
UPS components for maintenance purposes.

Important considerations:

– Is There an Input / Output Voltage Phase Shift?
– Can The UPS Be Tested?
– Overcurrent Protection?
– What Is Your Competition Quoting?

Maintenance Bypass Configurations

2-Breaker maintenance
bypass configuration.

– Normal operation MBB is
OPEN and MIB is closed.

– Input feed must be the same
as the UPS static bypass
feed.

– Three (3) input feeds for dual
input UPS.

– Be wary of single input UPSs -
PHASE SHIFTS!!

2-Breaker Maintenance Bypass
GOTCHA!!!

2-Breaker maintenance bypass
with “D” or “E” version of the
Npower UPS.

– UPS has a 30 degree phase
shift from input to output.

– Feed through the maintenance
bypass will be out of phase from
the UPS output.

– Always verify that the UPS
output will be in phase with the
maintenance bypass utility
feed!!!

Maintenance Bypass Configurations

3-Breaker maintenance
bypass configuration.

– Most commonly used.

– Two (2) input feeders for a
dual input UPS.

– Always know if bypass power
is available

– For single input UPS BIB
breaker must be sized for
UPS input current.

Sample UPS System with 3-Breaker
Maintenance Bypass

Maintenance Bypass Configurations

4-Breaker maintenance
bypass configuration

– Option for dual input UPS only.
– One (1) feeder for a dual input

UPS.

• No feeder redundancy

– RIB sized according to UPS
AC input current demand

Sizing Maintenance Bypass For
Single Module UPSs (SMSs)

Normally Based On 80% Rated Devices

(NFLA x 1.25) + (MA - NFLA) = Target Device Rating For Breaker
Feeding UPS Rectifier

(NFLA x 1.25) = Target Device Rating For Breaker Feeding UPS
Bypass Or Output Breaker

Information Required From Site Planning Document

– NFLA = UPS Normal Full Load Current

• NFLA = Rectifier Input Current for AC Input Device; Bypass or
Output Current for Device Feeding UPS Bypass or Serving as
Output Overcurrent Device.

– MA = Maximum Input Current

• MA = UPS Input Full Load Current PLUS Maximum Battery
Recharge Current

Solenoid Key Interlock System

Interlock System for
maintenance bypass
arrangements.

– Enforces proper transfer
sequence between UPS
output and maintenance
bypass source.

– Prevents UPS inverter from
being paralleled with the
bypass utility source.

– Will not prevent load dump.

Solenoid Key Interlock System

Includes the following components:

– “Kirk Key” locks on MIB and MBB breakers

– Solenoid Key Release Unit (SKRU)

– Communication interface kit required on most UPS modules to
communicate to the SKRU if the UPS is in the proper mode to
allow transfer to or from maintenance bypass.

Key is held captive in the SKRU until a permissive signal
received from UPS.

Transfer procedures are provided on the bypass
assembly to inform the user how to accomplish the
transfers.

Load Bank Breaker

Load Bank Breaker Option

– Bussed off UPS side of MIB
breaker. Sometimes
interlocked with MIB.

– Used for battery and UPS
load testing.

– UPS static bypass can’t be
tested when used with a 3-
breaker MBP.

Load Distribution Option

Load Distribution Breaker
Option

– Individual circuit breakers
provided in lieu of a single
main lug output.

– Limited space available in
Liebert matching maintenance
bypass cabinets.

EPO Option

Emergency power off
option for maintenance
bypass.

– Guarantees power shut
down under all conditions.

– Includes shunt trips on MIB
and MBB breakers

Maintenance Bypass Summary

Totally isolate the UPS cabinet for maintenance ~
Know the available feeders for the UPS system ~
Recommend interlock options ~
EPO requirement ~
Load bank breaker option ~
Load distribution option~