UNDERFREQUENCY RELAY

• US 3,558,911 A
• Filed: 05/29/1969
• Issued: 01/26/1971
• Est. Priority Date: 05/29/1969
• Status: Expired due to Term

• Current Assignee: Muchuan M. Chen
• Original Assignee: Muchuan M. Chen
• Inventors: Chen, Muchuan M.
• Application Number:
  US04/828,967
• Time in Patent Office: 607 Days
• US Class Current: 307/129
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
• CPC Class Codes: G01R 23/15 Indicating that frequency of pulses is either above or below a predetermined value or within or outside a predetermined range of values, by making use of non-linear or digital elements (indicating that pulse width is above or below a certain limit)
• CPC Class Codes: H02H 3/46 responsive to frequency deviations

Abstract

A digital underfrequency relay for load conservation and the like is provided. The relay monitors power system frequency, and when a subnormal frequency below a preset limit is detected a cyclic control signal is produced. This condition must persist continuously for a predetermined period of time before the relay will issue an underfrequency indicating output signal, and the requisite timing is accomplished by means substantially unaffected by variations in frequency during the delay period.

Claims

1. In a relay for monitoring the frequency of a periodic signal, said frequency under normal conditions being inside a preset limit and said relay being arranged to issue an output signal in response to certain abnormal frequency conditions, the combination of:

a. a frequency rEsponsive circuit adapted to be energized by said input signal and operative to produce a control pulse for each cycle of said input signal whenever the frequency thereof is outside said limit;

b. time delay means coupled to said frequency responsive circuit and operative to issue said output signal a predetermined time after activation thereof unless earlier disabled, said time delay means being activated in response to a control pulse being produced by said frequency responsive circuit and, once activated, being arranged to continue its timing operation independently of the frequency of subsequent control pulses; and

c. means for disabling said time delay means and thereby preventing issuance of said output signal in response to the frequency of said input signal returning inside said preset limit.

2. The relay defined in claim 1 in which said frequency responsive circuit is arranged to produce control pulses when the frequency of said input signal is under said preset limit.

3. The relay defined in claim 2 in which said time delay means includes means for adjusting the length of said predetermined time.

4. The relay defined in claim 3 in which an electronic counter is connected between said time delay means and said frequency responsive circuit, said counter being preset to activate said time delay means when a predetermined number of control pulses are consecutively produced.

5. The relay defined in claim 4 in which said time delay means comprises the series combination of a capacitor and a rheostat adapted to be energized by constant voltage upon activation of the time delay means, and means for issuing said output signal in response to the voltage across said capacitor attaining a predetermined level.

6. The relay defined in claim 2 in which said disabling means is normally operative to periodically disable said time delay means, said disabling means including means coupled to said frequency responsive circuit and activated by the control pulses for inhibiting operation of the disabling means so long as the interval between successive control pulses is shorter than the normal operating period of said disabling means.

7. In a relay for monitoring the frequency of a periodic input signal having a predetermined normal frequency, said relay being arranged to issue an output signal in response to certain abnormal frequency conditions, the combination of:

a. a frequency responsive circuit adapted to be energized by said input signal and operative to produce a first train of control pulses having a frequency correspondence to the input signal whenever the frequency thereof is under a predetermined first level and to produce a second train of control pulses having a frequency correspondence to the input signal whenever the frequency thereof is under a predetermined second level, said second level being lower than said normal frequency and said first level being lower than said second level;

b. first means coupled to said frequency responsive circuit for issuing said output signal in delayed response to said first train of control pulses being produced;

c. means for disabling said first means and thereby prevent issuance of said output signal in response to the frequency of said input signal returning above said first level; and

d. second means operative independently of said disabling means for normally terminating said output signal, said second means being coupled to said frequency responsive circuit and having its normal operation inhibited while said second train of control signals is being produced and for a predetermined interval of time following return of said input signal frequency above said second level.

8. The relay defined in claim 7 in which said second means includes means for adjusting said predetermined interval of time.

9. The relay defined in claim 7 in which said first means is operative to issue said output signal a predetermined time after activation thereof unless earlier disabled, said first means beIng activated in response to a control pulse in said first train and, once activated, being arranged to continue its timing operation independently of the frequency of subsequent pulses in said first train.