Motor controller with instantaneous trip protection
AssigneeSiemens Energy & Automation, Inc.
InventorSamir F. Farag
Life of this patent
Estimating the term…
Abstract
A motor control unit for protecting a motor against overload, short circuit and ground fault currents. The unit monitors the currents in each phase of the motor to provide values representative of each phase current. The unit also includes a contactor for opening and closing each phase, wherein the unit controls the contactor based upon the values representative of the phase currents. The contactor is opened where the phase currents exceed limits which indicate that either an overload, short circuit or ground fault situation exists at the motor. A magnetic trip circuit breaker can also be provided to operate in cooperation with the unit to provide instantaneous trip protection for current levels which are relatively high in relation to those for which the contactor is rated.
Claims29
A method of sensing unacceptable current levels in a motor control system having a motor coupled to at least two phases, comprising the steps of:
- continuously generating a first signal indicative of the current level in a first phase;
- continuously generating a second signal indicative of the current level in a second phase;
- continuously determining the greater of the first and second signals;
- continuously comparing the greater signal to a designated trip limit;
- generating a trip signal upon the greater signal exceeding the trip limit;
- disengaging the motor from the phases in response to the generation of a trip signal within a first designated period of time;
- and
- disengaging the motor from the phases in response to the current level in one of the phases exceeding a predetermined current limit for a second designated period of time which is shorter than the first designated period of time, wherein the trip limit corresponds to a current level lower than the predetermined current limit.
A motor control for sensing unacceptable current levels in a motor control system having a motor coupled to at least two phases, comprising:
- means for continuously generating a first signal indicative of the current level in a first phase;
- means for continuously generating a second signal indicative of the current level in a second phase;
- means for continuously determining the greater of the first and second signals;
- means for continuously comparing the greater signal to a designated trip limit;
- means for generating a trip signal upon the greater signal exceeding the trip limit;
- first means for disengaging the motor from the phases in response to the generation of a trip signal within a first designated period of time;
- and
- second means for disengaging the motor from the phases in response to the current level in one of the phases exceeding a predetermined current limit for a second designated period of time which is shorter than the first designated period of time, wherein the trip limit corresponds to a current level lower than the predetermined current limit.
A motor control for sensing unacceptable current levels in a motor control system having a motor coupled to at least three phases, comprising:
- means for continuously generating a first signal indicative of the current level in a first phase;
- means for continuously generating a second signal indicative of the current level in a second phase;
- means for continuously generating a third signal indicative of the current level in a third phase;
- means for continuously determining the greatest of the first, second and third signals;
- means for comparing the greatest signal to a designated trip limit;
- means for generating a trip signal upon the greatest signal exceeding the trip limit;
- first means for disengaging the motor from the phases in response to the generation of a trip signal within a first designated period of time;
- and
- second means for disengaging the motor from the phases in response to the current level in one of the phases exceeding a predetermined current limit for a second designated period of time which is shorter than the first designated period of time, wherein the trip limit corresponds to a current level lower than the predetermined current limit.
An apparatus for sensing ground fault and unacceptable current levels in a motor control system having a motor coupled to at least two phases, the apparatus comprising:
- means for continuously generating a first unrectified signal indicative of the current level in a first phase;
- means for continuously generating a second unrectified signal indicative of the current level in a second phase;
- means for continuously generating, from the fist and second unrectified signals, an unrectified sum signal indicative of the sum of the current levels;
- means for rectifying the sum signal;
- first means for continuously comparing the rectified sum signal to a designated limit;
- first means for generating a trip signal upon the rectified sum signal exceeding the limit for more than a predetermined period;
- means for continuously rectifying the first and second unrectified signals;
- means for continuously determining the greater of the rectified first and second signals;
- second means for continuously comparing the greater signal to a designated trip limit;
- second means for generating a trip signal upon the greater signal exceeding the trip limit;
- wherein said first means for generating a trip signal and said second means for generating a trip signal are simultaneously operable;
- first means for disengaging the motor from the phases in response to the generation of a trip signal within a first designated period of time;
- and
- second means for disengaging the motor from the phases in response to the current level in one of the phases exceeding a predetermined current limit for a second designated period of time which is shorter than the first designated period of time, wherein the trip limit corresponds to a current level lower than the predetermined current limit.
An apparatus for sensing ground fault and unacceptable current levels in a motor control system having a motor coupled to at least three phases, the apparatus comprising:
- a first current transformer disposed to continuously generate an unrectified first voltage substantially proportional to the current level in the first phase;
- a second current transformer disposed to continuously generate an unrectified second voltage substantially proportional to the current level in the second phase;
- a third current transformer disposed to continuously generate an unrectified third voltage proportional to the current level in the third phase;
- first means for continuously generating, from the first, second and third voltages, an unrectified sum signal indicative of the sum of the current levels;
- first means for rectifying the sum signal;
- means for continuously comparing the rectified sum signal to a designated limit;
- means for generating a trip signal upon the rectified sum signal exceeding the limit for more than a predetermined period;
- means for rectifying each of the first, second and third voltages;
- means for determining the greatest of the rectified first, second and third signals;
- means for continuously comparing the greatest signal to a designated trip limit;
- second means for generating a trip signal upon the greatest signal exceeding the trip limit;
- first means for disengaging the motor from the phases in response to the generation of a trip signal for a first designated period of time;
- and
- second means for disengaging the motor from the phases in response to the current level in one of the phases exceeding a predetermined current limit within a second designated period of time which is shorter than the first designated period of time, wherein the trip limit corresponds to a current level lower than the predetermined current limit.
Dependencies are inferred from the claim text.