Description

Masterclad metal-clad indoor switchgear is UL/cUL certified.

The number of bays in a Masterclad switchgear assembly depends on customer specifications. Each bay is a separate rigid, self-contained, bolted structure fabricated of heavy gauge steel. It consists of:

Front section with secondary control devices
Circuit breaker section, drawout voltage transformer and control power transformer, and fuse drawout section
Main bus compartment
Cable compartment

Upper and Lower Circuit Breaker Sections with Circuit Breakers Removed

Front Section

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

Circuit Breaker Section

The circuit breaker section contains sixteen separate, but coordinated, features, each necessary for circuit breaker operation:

Circuit breaker positioning rails
Racking mechanism
Circuit breaker position indicator
Disconnect position latch
Circuit breaker interlocks
Compartment rating interlocks
Control power receptacle
Ground and test unit and dummy circuit breaker interlock
Primary high voltage contacts
Current transformers
Shutters
Barriers
Section interlock
Ground contact bar
Mechanism-Operated Contacts (MOC)-circuit breaker positioning rails-optional
Truck-Operated Contacts (TOC)-optional

Circuit Breaker Positioning Rails

The circuit breaker is equipped with rubber wheels for moving the circuit breaker when it is outside the switchgear and metal rollers to guide and position the circuit breaker inside the circuit breaker section. The four metal rollers are captured in rails (see Circuit Breaker Floor Plate, Racking Device, and Interlocks) which position the circuit breaker in the vertical position.

Racking Mechanism

The racking mechanism (see Circuit Breaker Floor Plate, Racking Device, and Interlocks) is located on the circuit breaker section floor. It is operated by a removable racking crank inserted into the front of the circuit breaker section. The front door may be either open or closed. The circuit breaker engages in a gear-driven racking roller (see Circuit Breaker Floor Plate, Racking Device, and Interlocks). As the roller rotates, it moves the circuit breaker from the test disconnect to the connect position.

NOTICE
damage to Racking Mechanism Verify the torque required to rack a circuit breaker into the connected position on the first attempt to install a circuit breaker in the section. If using an electric racking device, verify the output to ensure the section racking mechanism will not be damaged from over-torquing. The torque limiter on the electric racking option is set at the factory at 18 lb-ft. (24.4 N•m). Failure to follow these instructions can result in equipment damage.

NOTICE

damage to Racking Mechanism

Verify the torque required to rack a circuit breaker into the connected position on the first attempt to install a circuit breaker in the section.
If using an electric racking device, verify the output to ensure the section racking mechanism will not be damaged from over-torquing. The torque limiter on the electric racking option is set at the factory at 18 lb-ft. (24.4 N•m).

Failure to follow these instructions can result in equipment damage.

The racking mechanism can be damaged by over-torquing due to high resistance from the circuit breaker/section connection points or any obstruction in the section that blocks free movement of the circuit breaker through the guide rail by the racking mechanism. The section racking mechanism is designed for 18 lb-ft. (24.4 N•m) of maximum torque. Exceeding the maximum torque will damage the racking mechanism.

Circuit Breaker Interlocks

A racking block bar (see Circuit Breaker Floor Plate, Racking Device, and Interlocks) welded to the racking shaft hits an interlock pin on the circuit breaker when it is closed. This interlock mechanism stops a closed circuit breaker from being moved between the test/disconnected position and the connected position.

The racking roller actuates an interlock located underneath the circuit breaker. This interlock mechanism is designed to stop a circuit breaker from being closed when it is between the test/disconnected and connected positions.

Circuit Breaker Floor Plate, Racking Device, and Interlocks

Callouts for the figure above are:

A	Circuit breaker position latch bracket	H	Racking block bar
B	Circuit breaker positioning rail	I	Section key interlock provision
C	Ground contact bar	J	Lockout lever
D	Racking block lever	K	Spring discharge bracket
E	Racking roller	L	Racking mechanism
F	Shutter actuator	M	Control power receptacle handle
G	Circuit breaker position indicator	N	Control power receptacle

A lockout lever located on the drawout gear box stops the circuit breaker from being inserted into the section when the racking roller is not in the test position.

A racking block lever blocks the racking mechanism from operating when the circuit breaker is not in the section. Without the circuit breaker in the section, the shutter cannot be opened.

A spring discharge interlock discharges the closing springs when the circuit breaker is inserted or withdrawn from the section.

CAUTION
interlock DAMAGE Do not test interlocks by hand. Test interlocks only by moving the circuit breaker over the section-mounted operating cams. Do not operate interlocks in an incorrect sequence. Failure to follow these instructions can result in injury or equipment damage.

Compartment Rating Interlocks

These interlocks block insertion of circuit breakers with incorrect current, voltage, or interrupting ratings into the compartment. The stationary interference brackets are mounted on the floor of the compartment and the moving part of the interlock system is mounted on the underside of each circuit breaker.

Ground and Test Unit Dummy Circuit Breaker Interlock

Each circuit breaker section is equipped with a ground and test unit (GTU) and dummy circuit breaker permissive interlock. GTUs and dummy circuit breakers that are not equipped with the required ground and test unit interlocks cannot be inserted into the circuit breaker section. The permissive interlocks are located beside the position interlock on the circuit breaker section floor. Refer to the specific GTU and dummy circuit breaker instruction bulletins.

Control Power Receptacle

The circuit breaker control power receptacle is located on the lower right floor of the compartment (see Circuit Breaker Floor Plate, Racking Device, and Interlocks and Circuit Breaker Section without Circuit Breaker). The molded insulating receptacle contains twenty-four contacts and two tapered guide pins. The control power can be connected in the test position by rotating the control plug handle and pulling it forward.

Circuit Breaker Section without Circuit Breaker

Disconnect Position Latch

A spring-loaded latch on the circuit breaker engages behind the circuit breaker latch brackets on top of the left-hand guide rail (see Circuit Breaker Floor Plate, Racking Device, and Interlocks) when the circuit breaker is in the test/disconnected position. The latch is disengaged by the circuit breaker release handle (see Circuit Breaker Release Handle) when the circuit breaker is in the test/disconnected position.

Circuit Breaker Release Handle

Shutters

Two steel shutters (see Circuit Breaker Section without Circuit Breaker) are mounted directly in front of the primary high voltage contacts. The shutters move with a rotary motion, actuated by the racking mechanism. Circuit Breaker Floor Plate, Racking Device, and Interlocks shows the shutter actuator.

Circuit Breaker Section without Circuit Breaker

Circuit Breaker Position Indicator

An indicator beside the racking port (see Circuit Breaker Floor Plate, Racking Device, and Interlocks, Racking Port, Handle, and Section Position Indicator, and Circuit Breaker Section without Circuit Breaker-Shutter Forced Open) shows which position the circuit breaker is in: test/disconnected, transport, or connected. When the door is open, two arrows which line up with the front cover are visible on the left hand rail. They also indicate the position of the circuit breaker.

Racking Port, Handle, and Section Position Indicator

Primary High Voltage Contacts

The primary main contacts are housed in a bell assembly (see Circuit Breaker Section without Circuit Breaker-Shutter Forced Open) consisting of insulating tubes extending toward the front. The current transformers are mounted around the bell assembly tubes which are covered at the open end by the shutter when the circuit breaker is in the test/disconnected position or is withdrawn from the section. The bell assembly is furnished with molded fiberglass polyester tubes as standard, but may also be equipped with optional porcelain tubes.

Circuit Breaker Section without Circuit Breaker-Shutter Forced Open

Current Transformers

Bushing-type, single- or multi-ratio current transformers (see Circuit Breaker Section without Circuit Breaker-Shutter Forced Open) can be mounted around either the top or bottom insulating tubes. A maximum of four current transformers, depending on accuracy, can be mounted per phase: two on the line side and two on the load side.

Section Interlock

A section key interlock provision (see Circuit Breaker Floor Plate, Racking Device, and Interlocks) is provided in each circuit breaker section for locking a circuit breaker out of the connected position. The section interlock is located in the center of the section floor and has padlock provisions as standard. It can be equipped with a key interlock when specified by the user. The section interlock blocks racking the circuit breaker into the connected position. A circuit breaker can be stored in the test/disconnected position with the section interlock locked.

Ground Contact Bar

A ground contact bar is located on the bottom of the circuit breaker section. It is directly connected to the main ground bus. A mating set of sliding contacts is located on the underside of the circuit breaker. The contacts engage before the circuit breaker reaches the test position and stay continuously grounded to the connected position.

Mechanism-Operated Contacts (MOC) (Optional)

Mechanism-operated contacts (see Circuit Breaker Section without Circuit Breaker and Mechanism and Truck-Operated Contacts) are compartment-mounted, auxiliary contacts operated by the circuit breaker mechanism. Like circuit-breaker-mounted auxiliary contacts, they indicate whether the circuit breaker is in the open or closed position. They operate in both the connected and test/disconnected positions.

The MOC unit is mounted on the left side of the circuit breaker section. It is operated by a mechanism that is driven vertically by a roller on the left side of the circuit breaker.

Mechanism and Truck-Operated Contacts

Truck-Operated Contacts (TOC) (Optional)

Truck-operated contacts (see Racking Port, Handle, and Section Position Indicator and Mechanism and Truck-Operated Contacts) indicate the physical position of the circuit breaker in the compartment. They indicate whether the circuit breaker is in the connected or test/disconnected position.

The TOC unit does not distinguish between the circuit breaker being in the test/disconnected position or withdrawn completely from the compartment.

The TOC unit is mounted on the right side of the horizontal steel barrier in the top of the circuit breaker section. It is operated by a spring-loaded lever. This lever is activated, just before the circuit breaker reaches the connected position, by a pin on the upper right side of the front cover of the circuit breaker.

Voltage Transformer, Control Power Transformer, and Fuse Drawout Units

The voltage transformer (VT), control power transformer (CPT), and fuse drawout units are self-contained drawers (see Drawout Units in Connected Position) that roll from the disconnected to the connected position. The drawer front panel is recessed behind the front door in the connected position and is held in place by two thumbscrews.

An insulating barrier (see Drawout Units in Connected Position) divides the compartment. The stationary contacts (see Drawout Units in Connected Position) and associated high-voltage parts are mounted behind the barrier. Floating, self-aligning line contacts engage the moving contacts as the drawer is inserted into the connected position. As the drawer is withdrawn, a static ground contact mounted on top of the compartment grounds the primary connection.

Drawout Units in Connected Position

Drawout Control Power Transformer

The control power transformer (CPT), Drawout Units in Connected Position, Control Power Transformer-Secondary Circuit Breaker Interlock, and Control Power Transformer-Secondary Contacts, supplies control voltage for circuit breaker closing, capacitor trip charging, and miscellaneous station auxiliary power functions. The transformer is sized for the specific order requirements. Do not add arbitrary non-specified loads after installation. The maximum capacity of the CPT in a drawout unit is 15 kVA.

The CPT, its primary current limiting fuses, and secondary molded case circuit breaker are mounted on the drawer and are withdrawn as an assembly. The secondary circuit breaker handle must be in the OFF position in order to withdraw or insert the drawer. To release the latch, push the secondary circuit breaker handle to the left (OFF position). To engage the latch, push the secondary circuit breaker handle to the right (ON position) after returning the assembly to the connected position.

Each drawout control power transformer is equipped with a padlock provision (see Control Power Transformer-Secondary Circuit Breaker Interlock) which locks the unit in the engaged position.

Control Power Transformer-Secondary Circuit Breaker Interlock

Secondary molded plug contacts are mounted on the front left side of the drawer (see Control Power Transformer-Secondary Contacts). They engage fixed-mounted contacts in the connected position.

Control Power Transformer-Secondary Contacts

Drawout Voltage Transformer

Drawout VTs (Drawout Voltage Transformer) supply voltage indication for metering and relaying purposes. Primary current-limiting fuses are mounted on each voltage transformer. Secondary molded plug contacts (see Drawout Voltage Transformer) are mounted on the front left side of the drawer and engage fixed compartment mounted contacts in the connected position. Secondary fuses for the voltage transformers are located in the front compartment.

Drawout Voltage Transformer

Drawout Fuse

Drawout fuses are provided for stationary control power transformers. Fixed-mounted CPTs are supplied when three-phase control power is required or control power requirements exceed 15 kVA. The current limiting fuses are mounted in the drawer and withdrawn as an assembly.

Drawout Primary Fuses for Stationary Control Power Transformer

The fuse drawout is interlocked with the secondary circuit breaker by a key interlock system. One interlock locks the drawout in the connected position. A second interlock allows the fuse drawout to be withdrawn only when the secondary circuit breaker is in the OPEN position. The secondary circuit breaker with interlock is mounted above or below the drawout unit.

Drawout Primary Fuses Interlock with Secondary Circuit Breaker

Secondary Circuit Breaker and Interlock for Drawout Primary Fuses

Main Bus Compartment

The main bus compartment is located 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 (see Two Bay Assembly-Rear View). The main bus compartment is accessible from the back (see Two Bay Assembly-Rear View) through the cable compartment and from the front through the circuit breaker section.

The 1200 and 2000 A, 50 kA main buses are available in aluminum or copper. The 3000 A, 50 kA and 1200, 2000, and 3000 A, 63 kA main bus is always copper.

Each bus bar has fluidized bed epoxy insulation rated for 221°F (105°C) operation. Glass polyester barriers are used to separate the bus compartments between adjacent sections. Optional porcelain inserts are available for 50 kA bus only.

Polyvinyl chloride boots insulate the connection in the main bus compartment, overlapping the epoxy insulation on the bus bars. The bus bar insulation and boots form an integral insulating system for the equipment to meet its dielectric ratings. The bus bar insulation must not be damaged or modified. Bus joint boots must be in place before energizing the equipment.

Cable Compartments

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

Two Bay Assembly-Rear View

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.

A typical ground bus cross section:

Up to 50 kA is 0.25 x 2.0 inch (6 x 51 mm)
63 kA is 0.5 x 2.0 inch (13 x 51 mm)

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

NOTE: Conduit should be stubbed in the concrete pad 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. This cable pull box may be removed to install the rear cables first. When required, zero-sequence current transformers (see Two Bay Assembly-Rear View) are conveniently located in each cable compartment.

Various cable termination systems are used. These are detailed on the plans and specifications. Solderless or compression lugs can be supplied on the load connectors. Potheads are mounted on grounded support brackets. The compound and tape for their internal connections are shipped in a container with other miscellaneous parts. Tape and insulating material necessary for completing the field connection at the bus pad are not supplied with the assembly.

Cable compartment floor plates must be removed, punched to fit the conduit, and reinstalled with the appropriate hubs. These floor components form a barrier and block vermin (rodents, snakes, insects) from entering the switchgear. Depending on the application, an appropriate seal putty may be required if there is not an alternative barrier elsewhere in the construction of the site.

The operating environment for Masterclad switchgear is described in Circuit Breaker Section Interlock System Operation, as “provide adequate ventilation at all times so the ambient temperature around the assembly does not exceed 104°F (40°C). Clean, dry filtered air should be supplied.” This means air with high humidity, such as air above standing water, or airborne particles, must be kept out of the switchgear enclosure. See Site Preparation, list of “Good site preparation”.

Surge Arresters

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.