FUNCTIONAL DESCRIPTION

Control Power

Control power of 24 Vdc/Vac, 32 Vdc/Vac, 48 Vdc/Vac, or 120 Vdc/Vac is

applied at terminals 1 and 2. (The MOC model number determines the

nominal input voltage level.) As necessary, it is rectified and decreased

to 24 Vdc at terminals 3 (negative) and 4 (positive). This 24 Vdc is applied

to the motor through a network of external switches which allow application

of the 24 Vdc in either polarity. The polarity is determined by the need to

raise or lower the system parameter controlled by the MOC.

Potentiometer Output

The potentiometer serves as the adjusting element of the MOC and is

connected to terminals 14. 15. and 16. The potentiometer wiper arm,

connected to terminal 15. moves toward terminal 14 when a raise

command is received. A lower command moves the wiper arm to move

toward terminal 16. Terminals 8 and 13 are connected internally to switches

that provide the centering feature for the potentiometer wiper arm.

INTRODUCTION

The MOC2XXX series of motor operated controls consists of a motor-driven,

variable potentiometer and the limit switches required to provide remote

adjustment of resistance or voltage. MOC2XXX controls can be specified

for ac or dc operation with 24-, 32-, 48-, or 120-volt control power.

MODEL NUMBER DEFINITION

The model number for this series of MOCs consists of the prefix MOC2

followed by three digits. The first digit establishes the input control voltage.

The second and third digits establish the output control element

characteristics. Table 1 lists the available model numbers and the

corresponding operating characteristics. For example, MOC2305 has a

32 Vdc control input and a 500 ohm, 2 watt potentiometer.

The BE1-FLEX Protection, Automation, and Control System is configurable

for nearly any Power System application. The BE1-FLEX covers a wide 

application spectrum as it can be configured for any combination of available

functions. The large configurable touchscreen provides an application-specific

user interface. To support unknown future needs, the BE1-FLEX can simply

turn on extra functions, change or upgrade boards, field upgrade non-hardware

style options, and securely update firmware all without needing to remove it

from the installation.

OUTPUT C!RCUiTRY

The output amplifier produces either positive or negative signals tO drive the regulator 0 r exciter (as

required). The polarity of this signalis determined by the appropriate jumpering ofthe A-B Polarity

Fanning Terminal Strip.

OVER-ÉXCITATION LIMITINGD

a. Over-excitation limting provides an initial fast actlng limlt of the current at a pre-selected

high level (allowing for motor-starting, fault clearing, etc.). After a set period of time (Oto 60 sec-onds),

the limit will drop to a lower level to prevent field overheating.

b. The dc current output Of the exciter or regulatorwlll pass through a the dc transducer (T3 ) .

The ac output of T3 will always be proportional tO the input  This ac output is rectified,

adjusted and applied the lnverse Timer.

0 If an inverse time characteristic destred the lnverse Time Adjustment is set for th 巳 desired

time and the Fixed Time Adjustment set counter-clockwise (CCW) 10 zero time- Figure 2 . 2

illustrates the inverse time characteristics for three dlfferent settlngs Of the lnverse Time Adjustment

(fully CW Mid-Range. and fully CCW)

d. If fixed time characteristic is desired or required, the lnverse Timer is set fully CCW tO zero

time, while the Fixed Timer is set the desired time. After the selected timer has timed out, the

e current becomes limited at the delayed threshold limit.

POWER SUPPLY

a. The EL 200 senses the generator voltage through transformer T2. This transtormer has tapsa

for use with the following input voltages: 90-139. 180-264. 342-528. and 540-660 Vac, +10%, 50/60

Hz.

b. A on Of the transformer (T2) outputfeeds the regulated power supply t0 produce · 14 Vdc

and a . 14 Vdc output for operating the circuitry 、 The transformer (T2) a 0 provides refer-

ence signals to the VAR detector, the watt detector and power the dc transducer (transformer T3).

b. The VAR and Watt Detectors convert the ac inputs tO dc outputs which represent ()y polarity

and amplitude) the VAR and Watt components Ofthe generator output current. The output of 1h9

VAR detector passes through a tapped resistor network (Curve Selector) to the VAR Comparator.

The VAR Comparator makes a comparison Of the Curve Selector output W1th a dc reference

vo 《 tage- If the leading VAR component (generator current) is higher than the reference voltage,

the Comparator outputs a signal through the voltage regulator/exciter that 刂 cause an exatation

limiting and thus, prevent operation outside the limit. This VAR limitlng action would normally

produce a limiting threshold (Refer to Figure 1 一 1 ) that would approach being a horizontal line at the

. 04 to . 0 . 6 per unit level. To produce the desired output culve ， a Watt signal IS passed through

the Forward Watt Amplifier (non-linear) 10 the VAR Comparator. TO assure proper operation ， a

calibration circuit is provlded 巧 set up the proper levels of operation for a wide range input

current levels.

SAFETY

As with all electrical equipment, appropriate safety measures must be

taken when dealing with excitation equipment. High voltage is present

within the excitation cubicles; their magnitudes depend upon the

particular system. Opening the sources (e.g., disconnecting device 41)

does not completely disconnect the high voltages.

As long as the machine is still physically connected to the system, there

is a possibility that a safety hazard exists.

Every precaution must be taken when working at the excitation control

switchgear to ensure that all high voltages are isolated and avoided by

test personnel. In addition to the machine terminal voltage (460 Vac or

greater) at the excitation transformer, there may be other sources of

power entering the cubicles, such as 125/250 Vdc and/or 120/240 Vac

used to feed certain devices. A good rule to follow is to assume that all

connections are live and dangerous until proven otherwise and to avoid

all body contact with any of these voltages.

DESCRIPTION

a. The Basler Electric Minimum/Maximum Excitation Limiter (Model: EL 200 ) performs 0 func-

tions. As a maximum excltation limiter, it senses the field current output Of the voltage regulator

or static exciter and limits the field current tO prevent overheating . As a minimum excitation

limiter, it senses the leading volt-ampere-reactlve (VAR) output 引 the generator and limits

any funher decrease in 0 怡 tion ()s necessary) tO prevent IOSS Of synchromzation and end

iron heating dunng parallel operation.

b. The EL 200 Excitation Limiter has circular characteristic that is compatible with typical genera-

10r reactive capabilities as shown by Figure 1 . 1 

APPLICATION

The EL 200 Excitation Lim1ter can be used with the following Basler voltage regulators and excita-

tion systems: SSR ， XR2001 ， XR2 2 》 xR2003 ， SR-A Series, SR-F Series, SR-E Series SR-H

Series, SSE, and SER-CB. The EL 200 is designed for use on generating systems and can be

used on a synchronous motor or condenser 评 the procedures in Chapter 4 are followed exactly.

Additionally, the Basler Electric EL 300 has been designed to fu 《 fll 《 moSt mOtOr applications

and is preferred over the EL 200 for this type Of appncation.

THEORY OF OPERATION

Rectifier diodes mounted on the rotor of a brushless generator or motor

fail by either opening or shorting. If a rectifier shorts, very high current

flows through the associated exciter armature winding and causes

excessive heating and probable failure of the exciter.

If a rectifier opens, the voltage regulator will substantially increase the

excitation to maintain the operating level. This constant, high level of

excitation could lead to failure of the regulator.

The EDM-200 determines the status of the rotating rectifiers by sensing

the ripple content of the exciter field current. The waveform shown in

Figure 2A is the normal ripple measured with all diodes functional.

Figure 2B illustrates a waveform where one diode is open. Figure 2C

illustrates a waveform where one diode is shorted.

Automatic Gain Controlled Amplifier

As the output of the input amplifier varies from 1 to 4 volts, the associated

ripple content also varies. To prevent the monitoring circuits from

interpreting the 1 to 4 volt change as a diode failure, the automatic gain

controlled amplifier offsets the signal variations so that the monitoring

circuit monitors the ripple in a constant amplitude signal.

VOLTAGE ADJUST CONTROL

a. An internal VOLT screwdriver adjust provides adjustment of the generator output voltage.

Clockwise rotation of this control will increase the generator output voltage.

b. The voltage regulator is shipped from the factory with a jumper connected across terminals 6

and 7. If a remote voltage adjust rheostat (R50) is used (supplied loose), the jumper across

these terminals should be removed and the remote voltage adjust rheostat should be connected

to these terminals. The wiper of the rheostat must be connected to the rheostat terminal which

connects to terminal 6 of the voltage regulator and the other terminals are connected as shown in

the interconnection diagram.

c. When the remote voltage adjust rheostat is adjusted to its maximum resistance (fully counter

clockwise), the minimum generator output voltage will be obtained. Also, when the remote

voltage adjust rheostat is use, the front panel VOLT control will operate as a voltage range adjust

control.

FREQUENCY COMPENSATION

The XR2002F (only) provides the following types of frequency compensation:

a. Volts-per-Hertz (V/Hz). This is a linear relationship between voltage and frequency and is

shown in Figure 1-1. This characteristic is generally used to improve system block load pick-up

performance by restraining the voltage recovery until the frequency has also started to recover.

A front panel UF ADJ control is used in conjunction with a VOLT control to provide adjustment of

the V/Hz characteristic along both the frequency axis (45 to 65 Hz) and the generator axis of

Figure 1-1. This characteristic factory preset at 55 Hz (60 Hz nominal).

b. Voltage Limited Volts-per-Hertz (VLV/Hz). This characteristic provides the advantage of

the Volts-per-Hertz characteristic during load application as well as allowing precise voltage

regulation during minor variations in generator speed. The “60 Hz” and “50 Hz” curves of Figure

1-1 represent the 60 Hz and 50 Hz VLV/Hz characteristic. The front panel UF ADJ control

provides adjustment of the corner frequency of both VLV/Hz characteristics along the frequency

axis of Figure 1-1.