Specifications

G20

GE Limitamp

Medium Voltage Motor Control

Components

Description

The Contactor Economizing Module (CEM) is a solid state

encapsulated module that is designed to apply the proper

voltage to pick-up and seal close GE CR193B, C, D and E

medium voltage vacuum contactors. The CEM performs the

same function as the older CTM, including the anti-pump

function, except it utilizes phase control SCRs to control output

voltage instead of a series capacitor.

The CEM is powered by 115 VAC nominal AC power, 50/60

Hz. Incoming power is to be applied to terminals “1” and “2”

of the module. Use a separate contact in series with the AC

power to switch the CEM (and contactor) on and off.

The CEM DC output terminals to the contactor coil are “3” (-)

and “4” (+). It is customary to place an additional series

switching contact directly in the coil circuit to minimize the

contactor drop-out time. When the DC coil current is inter-

rupted by this contact, the L/R coil time constant is greatly

reduced, shortening the drop out time of the contactor to

about 50 milliseconds. If this additional switching contact is

omitted, the contactor drop out time will be as much as 500

milliseconds. It is also recommended to place RC suppression

(SUPP, 0.1 MFD capacitor in series with 100 Ω resistor), cat.

no. 302A3847P1, directly across the contactor coil terminals

to reduce inductive “kick-back” voltages.

The CEM functions as follows: For one second after application

of 115 VAC to terminals “1” and “2”, the output voltage between

terminals “3” and “4” is in the range of 100 to 110 VDC when

the contactor coil is connected. After one second, the voltage

is reduced to 20 to 25 VDC for as long as AC power is applied.

When AC power is removed, the DC voltage is removed from

the contactor coil and the contactor drops out. The cycle is

repeated when AC power is reapplied to the CEM. The purpose

is to provide the high coil voltage for a long enough period

of time necessary to pick up the contactor (1 second) and

then transition to a much lower coil voltage to economically

maintain the contactor in a sealed closed condition. This

reduction in voltage reduces power consumption and greatly

reduces temperature rises in the coil.

Supp

Start-Stop

Control

CEM

Contactor Economizing Module