US 4,291,263 A · Amortisseur winding protection system

Abstract

This invention relates to a system for protecting an amortisseur winding during the starting of a synchronous motor. The system compares the actual slip frequency of the accelerating motor with predetermined slip frequencies. These predetermined slip frequencies are each associated with a timer which measures successive time segments. Each timer is stopped when the actual slip frequency, which decreases as rotor speed increases, is less than the associated predetermined slip frequency. When the timer is stopped a successive timer is started. In this manner the acceleration of the motor is broken up into time segments. The initial timer is started when the motor starts. The final timer is stopped when the rotor field current is applied to bring the motor into synchronism. Should any timer be permitted to have its timed segment expire before being stopped, the motor is shut down. There is also provided a thermal memory which receives information from the expired timer as to its associated slip frequency. This information is used to inhibit the motor from being restarted until the amortisseur winding has cooled. Previous systems were straight timing functions which crudely approximated the motor's acceleration. The present invention provides a system that more closely approximates the motor's non-linear acceleration characteristic.

Claims10

Dependent claims

A method of protecting an amortisseur winding during starting of a synchronous motor, said motor having a safe-time within which the motor accelerates to a speed near synchronous speed without damaging said winding, the method including the steps of:

sensing a characteristic of achieved motor speed,
providing a plurality of timing segments which measure succeeding periods of time within said safe-time,
associating with each timing segment a characteristic of desired motor speed above which said motor is required to accelerate prior to expiration of said timing segment,
comparing said achieved characteristic with said desired characteristic of each time segment so as to detect when achieved motor speed exceeds desired motor speed,
terminating each timing segment when its associated desired characteristic is exceeded by said achieved characteristic, and commencing a timing segment for measuring a succeeding period of time to the period of time measured by said terminating timing segment, and
stopping said motor in the event that the comparison of said achieved characteristic and said desired characteristic results in the achieved motor speed not exceeding the desired motor speed prior to expiration of the timing segment associated with said desired characteristic.

3 more elements

An apparatus for protecting an amortisseur winding during starting of a synchronous motor, said motor having a safe-time within which said motor accelerates to a speed near synchronous speed without damaging said winding, comprising:

means sensing a characteristic of achieved motor speed,
timing means providing a plurality of timing segments which measure succeeding periods of time within said safe-time,
comparing means associating with each timing segment a characteristic of desired motor speed above which said motor is required to accelerate prior to said timing segment expiring, said comparing means comparing said achieved characteristic and said desired characteristic of each timing segment so as to detect when achieved motor speed exceeds desired motor speed, and
said timing means responsive to said comparing means stopping said motor upon failure of said comparing means to detect the achieved motor speed exceeding the desired motor speed prior to expiration of said desired characteristic's associated timing segment.

1 more element

An apparatus for protecting an amortisseur winding during starting of a synchronous motor having a field winding and a safe-time within which said motor accelerates to a speed near synchronous speed, said apparatus comprising:

a sensor sensing slip frequency of the motor,
a plurality of timers measuring succeeding timing segments, each timing segment defining a period of time within said safe-time, each timer having an enable and an inhibit terminal, an enabling signal at said enable terminal commencing said timer, an inhibit signal at said inhibit terminal terminating said timer, each timer generating a trip signal upon the respective timing segment expiring prior to receiving an inhibit signal whereby said trip signal stops said motor,
a plurality of frequency detectors each having a frequency characteristic of desired motor speed to which said motor is required to accelerate within a timing segment of an associated timer, said detector generating an inhibit signal to said associated timer in the event that said slip frequency falls below said frequency characteristic of desired motor speed, each detector having associated therewith a succeeding timer to which it transmits an enable signal at the same time as transmitting an inhibit signal to said associated timer,
a first enable signal generated in response to the motor starting so as to enable a first timer of said timers, and
a last inhibit signal generated in response to a current being applied to said field winding so as to inhibit a last timer of said timers.

2 more elements

Dependencies are inferred from the claim text.

Amortisseur winding protection system

Life of this patent

Amortisseur winding protection system

Life of this patent

Abstract

Claims10