Basler Electric SCP 250 Var/Power Factor Controller

INTRODUCTION

The SCP 250 controls generator (SCP 250-G) or motor (SCP 250-M) power factor or vars by monitoring

the voltage and current and supplying a control input to a voltage regulator.

When the SCP 250 is controlling vars, the voltage regulator (or static exciter) output changes to attain the

selected reactive load current.

When the SCP 250 is controlling power factor, the voltage regulator adjusts the excitation until the

selected power factor is obtained.

The SCP 250 monitors the open/closed state of the circuit breaker so that the voltage regulator controls

excitation when the breaker is open and the SCP 250 controls excitation when the breaker is closed.

A voltage limiting feature in the SCP 250 prevents the voltage regulator from supplying full or no

excitation if utility power is lost and the peaking generator main breaker remains closed. Voltage limiting is

adjustable between ±10% and ±30%.

Because the SCP 250 is designed for behind-the-panel mounting, provisions are included for locating the

Var/PF switch and potentiometer remotely.

FEATURES

SCP 250 Var/Power Factor Controllers have the following features.

• Suitable for use in generator or synchronous motor applications

• Provide system control over a wide range of loading conditions

• Accommodate standard voltage sensing inputs

• Front panel selection of either var or power factor control

• Do not require use of motor operated control

• Specifically designed to operate with the standard Basler SR , KR, selected AVCs, SSR regulator

series, and SSE static exciter-regulators

• During power factor control, reactive load changes automatically when kW load is changed

• Easily calibrated on site

• UL recognized and CSA certified

APPLICATION

The SCP 250 is suitable for use in generator peaking and synchronous motor applications.

Generator Peaking Application (SCP 250-G)

In peaking generator applications, the paralleling circuit of a voltage regulator presents large changes in

reactive current when the bus voltage changes by a relatively small amount. However, the regulator’s

ability to compensate for large changes in bus voltage can be exceeded. Two examples illustrate typical

problem areas.

Example 1. A generator equipped with a voltage regulator adjusted for 4% droop can

have a variation in var load from zero to 100% with a 4% decrease in bus voltage.

Further decreases in bus voltage would overload the generator.

Example 2. An increase in bus voltage can cause leading power factor conditions with

the associated danger of the machine pulling out of synchronization.

To minimize the possibility of either example occurring, the SCP 250 is used and adjusted for operation in

a “safe” region with either a regulated “fixed” var level or a “fixed” power factor. Thus, for a large change

in reactive current due to bus voltage changes, the operating generator is unaffected.

Synchronous Motor Application (SCP 250-M)

In synchronous motor applications, the SCP 250 allows the desired operating power factor to be pre

programmed so that the motor power factor remains constant during normal loading conditions. During

transient loading conditions, the SCP 250 makes corrective motor field excitation adjustments through a

regulator or exciter-regulator and thereby minimizes the possibility of synchronous pullout.