NRC Medium Voltage Circuit
Breaker Training
CHAPTER 3
CIRCUIT BREAKER
ELECTRICAL COMPONENTS
AND OPERATION
Learning Objectives
• Recognize and understand the function of electrical
components used in the circuit breaker control circuit.
• Describe the function of the anti pump circuit.
• p
Understand the operation of the auxiliaryy switch “a”
and “b” contacts.
• Understand the function of the protective relays and
how they interface with the medium voltage circuit
breaker to automatically trip (open) in the event of
abnormal condition.
• Name the two common protection relays used on
medium voltage breakers.
BASIC ELECTRICAL
OPERATION
• The secondary disconnect
provides power to the
breaker electrical
components
• The charging
g g spring
p g
normally charges
automatically
• The breaker can now be
closed and opened from
a local control switch on
the breaker cubicle door
or from a remote location
(Control Room).
ELECTRICAL COMPONENTS
• Each breaker manufacturer operating
mechanism design is different, but the
electrical components required to operate
the breaker all have similarities.
Therefore, basic schematics for the
control circuit for each manufacturer
generally are similar as well.
Components of a stored
energy electrical circuits
• Secondary control
Block or secondary
Components of a stored
energy electrical circuits
• ABB HK Secondary
disconnects
Components of a stored
energy electrical circuits
• Charging Motor
Components of a stored
energy electrical circuits
• Magne-Blast close coil
located under the
operating mechanism
Components of a stored
energy electrical circuits
• ABB HK Close coil
being removed from
th b
the breaker
k
• Located behind the
front cover
Components of a stored
energy electrical circuits
• Double trip
coil design on
a magne-Blast
breaker
Components of a stored
energy electrical circuits
• Auxiliary Switch (aux
switch)
• And an interlock
switch
Components of a stored
energy electrical circuits
• Position Operated
Switches
• Magne-Blast
Anti Pump Coil Or Relay
• Y Relay (Anti Pump): The Y relay is a parallel circuit to
the spring release coil. The anti pump relay is
energized at the same time as the close coil, this will
open the normally closed Y contact in the close circuit.
• The ppurpose
p of the Y Relay:
y If the breaker does not
close on the first attempt, and the close coil remains
energized, the “Y Relay” provides a lock out to prevent
the breaker from attempting another close. If the close
signal is initiated but not removed the breaker has the
potential to cycle through an endless close, trip, charge,
close and trip cycle (Pumping). The Y coil opens the Y
contact in the close circuit and as long as the close
signal is present the breaker can’t re-close.
Components of a stored
energy electrical circuits
• Y/ Anti Pump Relay
on a Magne-Blast
b k
breaker
Components of a stored
energy electrical circuits
• Latch Check Switch:
Electrical Charging
• The charging motor is in the skip tooth position of the ratchet
wheel and stops pushing the mechanism.
• The closing prop/latch is engaged.
• The timing cam is in a position, which allows the motor, cut off
bracket or actu1ator to move. This will actuate the switch contacts
• LSb,
LSb which opens the circuit to the charging motor disconnecting
power to the charging motor. And
• LSa, which closes indicating that the motor has completed its
charge.
• The trip latch moves to a set position in preparation for closing the
breaker.
• The trip latch moving to the set position actuates the latch check
switch LCS closing the contact and completing the circuit to the
spring release coil (Close Coil).
ELECTRICAL OPERATING
SEQUENCE DHP
ELECTRICAL OPERATING
SEQUENCE ABB HK
• The charging motor is
energized pin 2 and 5
on the secondary
disconnect
ELECTRICAL OPERATING
SEQUENCE ABB HK
• Close coil is energized
pin 6 and 7 on the
secondary disconnect
ELECTRICAL OPERATING
SEQUENCE ABB HK
• Close coil is energized
pin 9 and 10 on the
secondary
d disconnect
di t
NRC Medium Voltage Circuit
Breaker Training
CHAPTER 3A
CIRCUIT BREAKER
ELECTRICAL COMPONENTS
AND OPERATION
Learning Objectives
• Understand the function of the protective relays and
how they interface with the medium voltage circuit
breaker to automatically trip (open) in the event of
abnormal condition.
• N
Name th
the ttwo common protection
t ti relays
l usedd on
medium voltage breakers.
Protective Relays
• Circuit breakers designed to operate
below 600 volts use trip-units and/or
series connected elements built directly
into the circuit and are internal to the
breaker. This design becomes impractical
when dealing with higher voltages. Hence
the protective relay is incorporated.
PROTECTIVE RELAYS
• By using transformers to reduce large
currents and high voltages to lower
ranges (usually 0-5 amps and 120 volts),
very simple motors or electronic circuits
can be used to externally control circuit
breakers.
Types of Protective Relays
• Electromechanical/Induction:
Electromechanical relays can be classified
into instantaneous ((magnetic
g attraction))
and time-delay (torque-controlled) units.
Electromechanical/Induction
• Instantaneous units: This type of relay unit
may consist of a solenoid and plunger or a
solenoid and a hinged armature. Magnetic
attraction is the operating
p g force.
• Time-delay units: This type of unit consists of
an induction-disk or induction-cup that has a
magnetic field applied to it by two poles of an
electromagnet which produce eddy currents
in the disk or cup generating torque on the
moveable rotor. A very simple motor.
Solid-state Relay
• These relays use electronic components to
provide protective functions similar to those
provided by electromechanical relays. This style
of relay employs discrete solid-state electronic
components and has no moving parts.
• Most versions of solid-state relays are simple
devices that provide a single function, such as
voltage, current, frequency, or phase angle
measurement similar to electromechanical
relays.
Microprocessor (Numerical)
Relay
• Microprocessor (Numerical): These devices provide
multiple protective functions in a single unit.
• The basic protection principles remain the same.
Microprocessor relays are also referred to as numerical
relays because they calculate algorithms numerically
• Basic construction consists of a microprocessor, an AC
signal data acquisition system, and memory components
containing the relay algorithms, contact inputs to control
the relay, and contact outputs to control other
equipment. The algorithms and settings contained in the
relay memory define the protection characteristics.
Instrument transformers
• The basic function is to change the magnitude (but not
the nature) of primary voltage and current to secondary
values to 120 volts and 5 or 1 amp where relays can be
applied.
• When relays compare the sum or difference of two or
more currents or the interaction of voltages and
currents, the relative direction of the current must be
known. The direction of current flow can be determined
by knowing the instrument transformer polarity. Polarity
markings are normally shown on instrument
transformers.
Current Transformers:
• Current transformers are designed for
connection in the primary circuit (either in
series or around the primary circuit). The
secondary current of the transformer
bears a known relationship with the
primary current.
Voltage Transformers
The purpose of the VT is to provide an
isolated secondary voltage that is and
exact proportionate representation of
primary voltage. ANSI standards for
accuracy are also established for VT’s.
Common switchboard protective
relay functions
• Over current relays
• Over-under voltage relays
• Directional relays
• Voltage or current balance relays
• Differential relays
Relays as applied to the
Switchboard
• Main Breaker protection
• Feeder circuit protection
• Relay
R l coordination
di ti
• Bus differential protection
• Transformer protection
• Motor circuit protection
Circuit breaker control
• Electro-mechanical and Solid-state relays:
Trip
p output
p contacts are connected in the
DC trip circuit of the relay or to the
operating coil of a lockout device which is
in turn connected to the breaker trip
circuit.
Circuit breaker control
• Microprocessor relays: Microprocessor relays have multiple output
contacts allowing direct trip control of the breaker for certain
protection elements and/or lockout trip control for other selected
elements. Outputs contacts may be connected in the closing circuit
of the breaker allowingg local or remote closingg operations
p through
g
the relay.
These relays are also equipped with input sensing circuits that can
be connected to breaker auxiliary contacts or cell switches so the
relay can monitor the breaker status (open/closed,
connected/disconnected). Numerous inputs are accommodated in
this type of relay allowing tremendous flexibility of control over a
circuit breaker. Custom logic can be applied in the relay software
for automatic operation of multiple circuit breakers.
Relay Settings
• Relay settings: The individual elements
that make up a protective relay are
adjustable. This is where sensitivity and
selectivityy are applied.
pp The level of
protection or pickup point is defined by a
setting. If applicable a time delay may
also be selected. Pickup settings options
are usually one of two formats, secondary
values or per-unit values.
Secondary values
• Example: An electromechanical time
over current relay has a 300:5 CT
connected to it. The pickup setting 3.3 is
the current that will be measured at the
relay terminals when 180 amps of primary
current passed through the CT. At that
time the induction disc will start to move.
Per-unit values
• A percentage of the CT rating
• Example: A microprocessor relay has a
300:5 CT connected to it. The per-unit
p
value of the above setting (180 amps
primary) is 0.6 x CT.
0.6 x 300 = 180 amps primary
0.6 x 5 = 3 amps secondary
Setting relays
• Electromechanical: Manually place screw in the desired tap on the
relay. Turn time-dial to the desired delay band.
• Solid-state: Usually setting a dial on the face for the relay for the
pickup and delay.
• Microprocessor: The easiest method is connecting a laptop to the
relay with required communication cable and utilizing the
manufacturer’s software to install protection and logic settings.
Settings files may be developed with OEM software without being
connected to a relay.
• These files can then be installed directly into the relay without
having to enter settings for each element individually.
Summary
Without the protective relay, the medium voltage
circuit breaker is nothing more than a switch. It needs
to be told when to close and when to open.
Technology offers us many new and innovative ways
to do just that
that. Despite all these terrific ideas we still
have relays that are 30-40 years old that need to
remain in service. There is quite a broad range of
protective devices one may encounter in a medium
voltage switchboard. What we have shown today is
only the tip of the iceberg. Protective relaying is a
science all its own.
