Siemens 3PCI Series, Operation Manual

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Introduction 3PCI SCR Power Controller Series Manual
1-2
s
Version 1.2 (19000325)
Figure 1-2. Front, Cutaway and Side Views of a Typical 25A to 225A 3PCI Controller
1.2. Operation
The 3PCI accomplishes phase fired control by the switching action of three pairs of inverse-parallel power
SCRs. The switching, or gating, of the SCRs is controlled by a digital firing control circuit synchronized “in
phase” with the line frequency (either 50 or 60 Hz). The digital firing circuit may be manually controlled by the
BIAS control, or automatically or manually controlled by one of several external methods.
Screwdriver-adjusted BIAS and GAIN controls are used to set up the 3PCI for operation by external control.
Chapter 3: Operation describes how to implement the various control methods.
1.3. Three-phase Overcurrent (OC) Trip Feature
The three-phase overcurrent trip (OC) feature provides circuit protection from output current overloads by
serving as a fast-gate shutdown. (OC functions similar to an electronic fuse.) The trip point is adjustable from
25% to 200% of the SCR power controller’s rating. Current transformers on the SCR power controller’s
output lines allow option OC to monitor instantaneous peak current. When the peak current level exceeds the
preset trip level, SCRs are gated off, and the load current is shut down within a half cycle. The TRIP RESET
push-button can be configured for automatic or manual reset to resume operation. See Section 4.5: Adjusting
the Overcurrent (OC) Feature.
The overcurrent (OC) feature is used mainly for the fuseless RF generator design (model RF3PI). The
leakage impedance (LZ) and the transformer’s maximum KVA determine what maximum thermal-rated
current power controller will be needed. Additional connections need to be made from the OC relay contact
and the customer’s circuit breaker or the plate contactor.
The OC feature shuts down the controller within the first half cycle of fault current. Then the overcurrent relay
opens the circuit breaker or plate contactor to clear the fault. For a fused design, the fuse will open at the
same time the OC feature trips. This feature is not recommended for fused designs.
To adjust the overcurrent (OC) feature, follow the instructions listed in Chapter 4: Options Setup.
Overcurrent (OC) trip relay contacts are available at terminals
TB2-40
,
TB2-41
and
TB2-42
.
1.4. Three-phase Current Limit (CL) Feature
The 3-phase current limit (CL) feature prevents the output current of an SCR power controller from exceeding
a preset maximum current level, as determined by the current limit control setting (5% to 125%). Current
*