Cutler-Hammer EATON Ampgard Mark V Manual de instrucciones - Página 2

Navegue en línea o descargue pdf Manual de instrucciones para Controlador Cutler-Hammer EATON Ampgard Mark V. Cutler-Hammer EATON Ampgard Mark V 12 páginas. Solid-state, brush-type, synchronous motor controllers

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SYNCHRONOUS MOTORS (Continued)

changing the field current can change the power factor at

which the synchronous motor runs or the reactive current

drawn from the AC line.

A synchronous motor cannot start with its DC pole

windings excited. Voltage is applied to the DC winding

only after the motor has been accelerated to a speed

which is over 90 percent of synchronous speed. With a

slip of less than ten percent, the DC poles will jump to

synchronous speed when DC voltage is applied and will

lock onto the rotating magnetic field produced by the

three-phase alternating current in the stator.

Applying DC at the most advantageous time is the job of

the motor controller which uses feedback signals to opti-

mize the transition and thereby minimize the disturbance to

the power system at the time of synchronization.

MOTOR FIELD EXCITATION

In this controller, the DC power for the excitation of a

synchronous motor field is obtained from a solid-state

power supply (exciter). Provisions are made for field

current adjustments. Usually, field current is set to

optimum values only after the motor field has reached

maximum operating temperatures. On cold start-ups, the

field current may be 20 to 40% high initially but will

decrease to normal as operating temperatures are

reached. The field current is usually maintained as set

during motor operation except where the field current

regulator option is included for those applications in which

VAR, power factor, or the field current itself is being

automatically adjusted.

THE MOTOR CONTROLLER

As explained in the companion instruction material, each

Ampgard

full-voltage motor starter (controller) consists of

one nonload-break isolating switch, one contactor, current-

limiting fuses, a set of current transformers, and some

form of overload protection. A reduced-voltage starter

includes all of the components of a full-voltage starter plus

one or two additional contactors and related control

components. A synchronous motor controller is either a

full-voltage starter or a reduced-voltage starter which

includes a source of DC and the additional controls

needed to start a synchronous motor, operate it at syn-

chronous speed, and protect it.

THE MARK V CONTROLLER

The Mark V is a field power supply and controller that

blocks the field voltage during subsynchronous operation

and applies the field voltage during synchronous operation.

The field voltage is adjusted by a potentiometer during

operation.

Fig. 1 Synchronous Motor Components

This solid-state field power source functions without

regard to the phase sequence of the three-phase power

supply, which may be at either 50 or 60 hertz. The field

power supply and controller contains synchronizing

circuitry with means to adjust the synchronizing slip-

frequency from 1 to 9 percent (SW1) and the permissible

stalled-rotor time from 0 to 9 seconds (SW2). It has pole

slippage sensing, incomplete sequence detection and

shutdown in the case of exciter low voltage or phase loss.

Figure 2 shows the solid-state field power supply panel

designed to control the application of either 125 VDC or

250 VDC to the field of a synchronous motor. The panel

consists of a printed circuit board (synchronizing control

board), protective fuses, and an assembly of power

thyristors (silicon controlled rectifiers, SCR's) arranged to

convert 120 or 240 VAC, three-phase, to 125 or 250 VDC,

respectively. The direct current (DC) is supplied directly to

the field of the synchronous motor. The synchronizing

control board shown in the lower portion of Figure 2

appears enlarged in Figure 3.

Characteristics

Each Mark V controller has a maximum DC current

capability (50, 100, or 200 amperes), a rated field supply

voltage of 125 or 250 VDC, and the ability to withstand a

field output (induced) voltage of up to 1500 volts during

the time that the motor is coming up to rated speed, i.e.,

I.B. 48008

Effective 11/97