Electric Power Generation, Transmission, and Distribution

Since the type B regulator is more common, the remainder of this section will address the type B step-
voltage regulator.
The tap changing is controlled by a control circuit shown in the block diagram of Fig. 21.14. The
control circuit requires the following settings:

1. Voltage Level—The desired voltage (on 120 V base) to be held at the ‘‘load center.’’ The load
   center may be the output terminal of the regulator or a remote node on the feeder.


2. Bandwidth—The allowed variance of the load center voltage from the set voltage level. The
   voltage held at the load center will be+^12 of the bandwidth. For example, if the voltage level is set
   to 122 V and the bandwidth set to 2 V, the regulator will change taps until the load center voltage
   lies between 121 and 123 V.


3. Time Delay—Length of time that a raise or lower operation is called for before the actual
   execution of the command. This prevents taps changing during a transient or short time change
   in current.


4. Line Drop Compensator—Set to compensate for the voltage drop (line drop) between the
   regulator and the load center. The settings consist ofRandXsettings in volts corresponding to
   the equivalent impedance between the regulator and the load center. This setting may be zero if
   the regulator output terminals are the load center.

The rating of a regulator is based on the kVA transformed, not the kVA rating of the line. In general
this will be 10% of the line rating since rated current flows through the series winding that represents
the+10% voltage change.

21.1.4.1 Voltage Regulator in the Raise Position

Figure 21.15 shows a detailed and abbreviated drawing of a type B regulator in the raise position. The
defining voltage and current equations for the type B regulator in the raise position are as follows:

Voltage equations Current equations

V 1

N 1

¼

V 2

N 2

N 1 I 1 ¼N 2 I 2 (21:77)

VS¼V 1 V 2 IL¼IsI 1 (21:78)

VL¼V 1 I 2 ¼IS (21:79)

V 2 ¼

N 2

N 1

V 1 ¼

N 2

N 1

VL I 1 ¼

N 2

N 1

I 2 ¼

N 2

N 1

IS (21:80)

Line Current

Voltage

Relay

Time

Delay

Motor

Operating

Circuit

Current Transformer

Line Drop

Compensator

Potential Transformer

FIGURE 21.14 Regulator control circuit.