Basler Electric 91747C0113 Minimum/Maximum Excitation Limiter

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.

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.

The AVC Sensing Module can be mounted directly on a genset using #10-32 or

equivalent hardware. A lock washer should be used between the screw head and

body of the module. Torque applied when tightening the mounting hardware

should not exceed 25 inch-pounds (2.8 N•m).

The AVC Sensing Module provides a convenient and cost-effective method

for expanding the applications where AVC63-12 and AVC125-10 voltage

regulators can be applied. The AVC Sensing Module increases the nominal

sensing voltage of style BX AVC63-12 and AVC125-10 voltage regulators

from 200/240 Vac to 480 Vac or 600 Vac. The AVC Sensing Module is

compatible with nominal sensing frequencies of 50/60 Hz and 400 Hz.

A compact, rugged (potted) case enables the AVC Sensing Module to be

mounted directly on the generator.

Other than making connections during installation, the AVC Sensing Module

requires no adjustment or calibration.

MOUNTING –40 to 70°C (–40 to 158°F) operation and storage 95%,

non-condensing 160 g (6 oz.)

The AVC Sensing Module is housed in a potted, plastic case that can be

mounted in any convenient position.

SPIKE SUPPRESSION MODULE

Some higher impedance power sources (such as power isolation transformers

and PMGs) may have enough inductance to cause potentially damaging voltage

spikes in the power output stage of the SSR Voltage Regulator. In these cases,

Basler Electric recommends the use of the Spike Suppression Module which was

supplied with the Regulator to filter out these potentially damaging voltage spikes.

Refer to Section 2 for mounting and interconnection instructions.