Introduction

The front section includes the front hinged doors with instruments, relays, control switches, terminal blocks, fuse blocks, and other required secondary control devices. It also houses the wiring space for inter-unit connection and customer control wiring connection.

The voltage transformer (VT) and fuse drawout units are self-contained drawers. As the drawout units are racked into the compartments, the drawers roll on two positioning rails mounted on the sides of the compartment. The rails capture and align rollers on drawout units.

Floating, drawer-mounted, self-aligning contacts engage the stationary primary contacts as the drawer is racked into the connected position.

A ground contact bar, located on the left guide rail, is directly connected to the main ground bus.

A sliding contact finger, located on the left side of the drawout units, engages the ground bar when the drawout unit is in the DISCONNECTED position and remains continuously grounded.

A static discharge ground contact, mounted in the top of the compartment, grounds the primary fuse contact tabs during withdrawal from the CONNECTED position to the DISCONNECTED position.

Control power transformers (CPTs) are always stationary mounted. Depending on the size of the transformer, they can be mounted remotely or within the switchgear.

The main bus compartment is in the center of the switchgear. It is isolated from other compartments by the main bus compartment cover, which consists of removable metal access plates. The main bus compartment is accessible from the back through the cable compartment and from the front through the circuit breaker compartment. The main bus is available in copper only.

Bus Compartment

Each busbar has epoxy insulation rated for 221°F (105°C) operation. Glass polyester barriers with epoxy insert pass-throughs are used to separate the bus compartments between adjacent circuit breaker compartments. Bus boots insulate the connection in the main bus compartment, overlapping the epoxy insulation on the busbars. The busbar insulation and boots form an integral insulating system for the equipment to meet its dielectric ratings. The busbar insulation must not be damaged or modified. Boots must be in place before operating the equipment.

Each circuit breaker in a vertical section has a separate cable compartment, accessible by removing a steel cover on the back. Insulated load connectors are provided for terminating cables. As standard, the load connectors are punched for terminating two cables per phase with a NEMA two-hole pattern.

A ground bus in the cable compartment has lugs on each end for the assembly ground. This ground bus is connected to each circuit breaker compartment ground contact bar and to the individual ground bars in each cable compartment. All instrument transformer, metering, and relaying grounds are also connected to this common ground system.

Conduit must enter the cable compartments, in the areas shown on the customer drawings (see Main Bus Connections, Side View), from either the top or bottom of the cable compartment. A removable steel cable pull box (see Bus Compartment) is provided to isolate cables when two circuit breakers are installed in one vertical section.

Conduit should be stubbed in the concrete as part of the site preparation before the assembly is installed, but top entrance conduit must be installed after the assembly is in place. The top covers can be removed, punched to fit the conduit, and put back in place.

The front conduit area is for the bottom circuit breaker when all cables enter from below, and for the top circuit breaker when all cables enter from above. The cable pull box may be removed to install the rear cables first. The cable pull-box must be reinstalled to provide isolation. When required, zero-sequence current transformers (see Bus Compartment) are conveniently located in each cable compartment.

Various cable termination systems are used. These are detailed on the customer’s plans and specifications. Solderless or compression lugs (provided upon request) can be supplied on the load connectors. Tape and insulating material necessary for completing the field connection at the lug pad are not supplied with the assembly.

Schneider Electric provides lugs upon request. Tape and associated material for insulating cable terminations are not supplied.

Surge arresters are furnished only when listed in the user’s specifications. The vulnerability of the incoming and outgoing lines to lightning strikes or other high voltage transient conditions determines their type and justification. Surge arresters, when specified, are mounted in the incoming and outgoing cable compartments. Surge arresters must remain disconnected from the main bus during start-up testing. Surge arresters are shipped from the factory disconnected from the main bus to help prevent damage during hi-pot testing prior to energizing. Connect surge arrestors after hi-pot testing and before energization.

The rating nameplate is located on the front of the circuit breaker and shows the circuit breaker rating.

The OPEN (O) / CLOSED (|) indicator (see Circuit Breaker, Front View with Circuit Breaker Cover) shows whether the vacuum interrupter contacts are OPEN (O) or CLOSED (|). The CHARGED/DISCHARGED indicator shows whether the closing springs are charged or discharged.

Circuit Breaker, Front View without Circuit Breaker Cover

The operating mechanism is a stored energy-type mechanism. It uses spring assemblies to perform circuit breaker openings and closing functions.

The closing spring assembly closes the circuit breaker when the CLOSE (|) pushbutton is pressed or when the close coil (see Trip and Close Coils) is energized. The spring assembly is charged (compressed) mechanically by the manual charging arm or electrically by the spring charging motor. When the control power is applied to the circuit breaker, the spring charging motor is energized. The charging motor turns the gear assembly which drives the ratchet assembly and compresses the closing spring assembly (see Left Side of Mechanism).

The opening spring assembly opens the circuit breaker when the OPEN (O) pushbutton is pressed, or the opening coil is energized. The spring assembly is compressed whenever the circuit breaker is in the CLOSED (|) position.

Vacuum interrupters are mounted vertically at the rear of the circuit breaker frame and perform the circuit breaker interruption.

Circuit Breaker, Side View

The primary connection to the associated switchgear is through the six primary disconnects mounted horizontally at the rear of the circuit breaker.

A typical schematic diagram for the control circuit of the Type VR circuit breaker is shown in Typical Control Circuit Schematic (Shown with Closing Spring Assembly Charged and Power OFF). The control circuit design may vary, depending upon customer requirements. Always refer to the specific schematic diagram for the specific Masterclad switchgear in question.

Typical Control Circuit Schematic (Shown with Closing Spring Assembly Charged and Power OFF)

The auxiliary switch (see Auxiliary Switch and Anti-Pump Relay) is a multi-stage switch used to operate circuits that depend on the position of the circuit breaker contacts. The schematic diagram in Typical Control Circuit Schematic (Shown with Closing Spring Assembly Charged and Power OFF) illustrates how each of the auxiliary switch contacts interconnect with the circuit breaker circuitry. The auxiliary switch functions as follows:

• Two Type-a auxiliary contacts connect in series with the trip coil. Because these stages are OPEN (O) when the circuit breaker is in the OPEN (O) position, the auxiliary contacts de-energize the trip coil when the circuit breaker is in the OPEN (O) position.

• The Type-b contact, connected in series with the closing coil, opens to de-energize the closing coil when the circuit breaker main contacts are in the CLOSED (|) position.

As shown, several Type-a and Type-b contacts are provided for optional use.

Auxiliary Switch and Anti-Pump Relay

The motor limit switch (see Motor Limit Switch) energizes the spring charging motor (see Circuit Breaker, Front View without Circuit Breaker Cover) when a closing spring charging operation is required. The motor limit switch de-energizes the spring charging motor when the closing springs reach the fully charged position.

As shown in the schematic diagram, the motor limit switch is connected to the motor in the normally OPEN (O) position. (see Typical Control Circuit Schematic (Shown with Closing Spring Assembly Charged and Power OFF)). When the closing springs are in the discharged position, the motor limit switch cam actuates the motor limit switch. This energizes the motor and disables the closing coil. Once the closing springs are fully charged, the cam allows the switch to assume the OPEN (O) position, de-energizing the spring charging motor.

Motor Limit Switch

When energized by the closing of the motor limit switch, the spring charging motor (see Left Side of Mechanism) drives the series of connected gears. These gears in turn raise and lower the ratchet assembly to compress the closing springs to the charged and latched position. When the closing springs are fully charged, the motor limit switch contacts reopen, de-energizing the spring charging motor.

Left Side of Mechanism

The latch check switch indicates that the circuit breaker is ready for subsequent operation.

If the closing coil circuit is continuously energized, the anti-pump relay (see Auxiliary Switch and Anti-Pump Relay) helps ensure that the circuit breaker does not “pump” OPEN (O) and CLOSED (|) if a a trip signal is also present. The anti-pump relay performs this function by allowing the closing coil to activate only if:

• The circuit is energized,
• The closing springs are fully charged,
• And the spring charging motor is de-energized.

The anti-pump relay activates when the close circuit is energized while the circuit breaker is closed. If the close circuit is energized continuously, the anti-pump relay remains in the energized position after the 52/a auxiliary contact closes during the closing operation. When the anti-pump relay is energized, a pair of its normally-closed contacts, in series with the close coil, open to help ensure that the close coil cannot be energized. The close coil activates only when the close circuit is de-energized (de-energizing the anti-pump relay), then energized again.

The standard location of the trip and close coils is in the upper center of the operating mechanism. When energized by the switchgear or remote circuitry, these coils release the open or close latches located inside the mechanism.

Trip and Close Coils

The motor cutoff switch is located under the base of the Type VR circuit breaker. The motor cutoff switch de-energizes the spring charging motor circuit during the installation of the circuit breaker or its removal from the compartment.