Trane ctv-prc007-en Options, Unit Mounted, Starter Cont, Available options include, SCR’s

Unit	Unit Mounted
Options	Starter (Cont.)

Available options include:

•Circuit Breaker — A standard interrupting capacity circuit breaker is available. The circuit breaker is mechanically interlocked to disconnect line power from the starter when the starter door is open.

•High Interrupting Capacity Circuit Breaker — A high interrupting capacity circuit breaker is available. This breaker is also interlocked to disconnect line power from the starter when the starter door is open.

•Circuit Breaker with Ground Fault — Ground Fault protection is available with either standard or high interrupting capacity circuit breakers. An indicating light is provided to indicate if a ground fault has occurred.

•Current Limiting Circuit Breaker — A standard circuit breaker incorporating the current limiters with fuse links is available. A fault current in excess of the circuit breaker capacity will blow the fuse links and interrupt the fault current. The circuit breaker cannot be reset until the blown current limiters are replaced.

•Ground fault detection and protection (available only with circuit breaker options)

The solid-state starter controls the starting characteristics of a motor by controlling the current that flow to the motor. It does so through the use of SCRs (Silicon Controlled Rectifiers), which are solid-state switching devices, and an integral bypass contactor for power control.

SCR’s

An SCR will conduct current in one direction only when a control signal (gate signal) is applied. Because the solid-state starter is for use on AC (alternating current), two SCR’s per phase are connected in parallel, opposing each other so that current may flow in both directions. For three- phase loads, a full six-SCR configuration is used. The connection is shown in Figure O-3.

During starting, control of current or acceleration time is achieved by gating the SCR on at different times within the half-cycle. The gate pulses are originally applied late in the half-cycle and then gradually applied sooner in the half- cycle. If the gate pulse is applied late in the cycle, only a small increment of the wave form is passed through, and the output is low.

Figure O-3 — Six-SCR Configuration

Figure O-4 — Wave Forms

If the gate pulse is applied sooner in the cycle, a greater increment of the wave form is passed through, and the output is increased. So, by controlling the SCR’s output voltage, the motor’s acceleration characteristic and current inrush can be controlled. These forms are shown in Figure O-4.

Integral Bypass Contactors

When the SCR’s are fully “phased on,” the integral bypass contactors are energized. The current flow is transferred from the power pole to the contactors. This reduces the energy loss associated with the power pole, which is otherwise about one watt per amp per phase.

When the starter is given the stop command, the bypass contactors are de- energized, which transfers the current flow from the contactors back to the power poles. Two-hundred fifty milliseconds later, the SCR’s are turned off, and the current flow is stopped.

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