Beckwith Electric M-0127A and M-0170A AC Current Relays

The M-0127A AC Current Relay guards against excessive circulating current using the circulationg current

method or the ∆VAR® 1 method. The M-0127A can be used in other current- and voltage-sensing

applications. Its adjustment range is 0.01 to 0.1 A.

• M–0127A intended for use in 0.2 A circulating current circuit of paralleled LTC transformers to guard

against damaging excessive circulating current

• M–0170A prevents damage to LTC transformer’s switching mechanism under excessive loads

• Available in:

• M–0127A: 0.01 to 0.1 Amps

• M–0170A: 0.2 to 0.4 Amps

• Both relays can be used in other current and voltage-sensing applications.

M‑0127A Application

The M‑0127A AC Current Relay is primarily designed as a recommended addition to the Circulating Current

or Delta VAr1 Paralleling configurations used with LTC Transformers. Its purpose is to monitor the current in

the circulating loop between transformers, and interrupt Motor Power to its monitored transformer, should

the circulating current exceed a predetermined value. The M‑0127A range permits the maximum circulating

current to be set from 5% to 50% of the rated full load current.

Other relays used for this purpose have an impedance exceeding 5.000 Ω which may cause the main CT to

saturate, making the entire circulating current scheme operate poorly. The low impedance of the M‑0127A

relay avoids this problem.

The output should be connected in series with the common lead of the automatic control circuit of the motor

starter relay. When used with the Beckwith Electric M‑0067E control, the M‑0127A output contacts will be

in series with the lead that would otherwise have gone directly to terminal TB1‑8 of the M‑0067E. Polarity

of the M‑0127A input and output can be ignored.

M‑0170A Application

The M‑0170A AC Current Relay is intended to be used in the load current circuit to prevent the tapchanger

from changing taps on excessive load current. Its range permits the current setting from 100% to 200% of

the rated full load current. The relay is connected in the same manner as the M‑0127A.

Additional Applications

The M‑0127A and M‑0170A can be used wherever an adjustable, low burden AC relay is required. They

have virtually no time delay, a very small hysteresis and a normally closed output for use on AC only. The

relay output draws approximately 6 mA of in‑phase current through a 120 Vac load when open. These factors

must be considered for the user’s specific application.

By adding external series resistors, the relays may be used for voltage sensing. For example, with a 10 K

series resistor, the M‑0127A is adjustable from 100 to 140 Vac, using 10 to 14 mA current setting range.

Use of a 10 K, 10 W wire‑wound resistor is suggested.