Richards 137NP, Инструкция по эксплуатации, Страница: 32 / 53

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G. Mechanical Indicator
The protector is equipped with a mechanical indicator to tell whether the protector is “open”
or “closed”. This mechanical indicator is operated by a linkage directly connected to the
breaker crosshead. It exposes either the word “OPEN” or the word “CLOSED”, depending
on the position of the breaker contacts. Provision is made for adjustment of the length of the
operating link.
H. Operating Mechanism
The mechanism for closing the breaker of the 137NP network protectors is of the gear-driven
cam, motor operated type. (see Figure 5). The operating motor is mounted on the worm and
gear housing to the left of the closing linkage. The motor drives the worm through a torque
brake which permits free running of the motor while torque is being transmitted from the
motor to the worm, and serves to stop the motor’s rotation immediately when the motor is
de-energized. The brake assembly serves as a coupling between the motor and worm shaft
and is mounted on the lower end of the motor shaft in the upper part of the gear housing.
Sequence of Operation
The sequence of operation of the 137NP network protectors may be best explained by
consideration of the simplified control diagram by Figure 12.
Assume that the breaker is open. The sequence on closure is as follows:
1. When the proper voltage conditions exist the relay will close its “closing contacts.
2. This action will energize the coil of the motor control device through the “b” and “c”
switches (assuming that the manually operated handle is in the automatic position).
3. The motor device will then close its contacts and energize the operating motor.
4. As the breaker closes, two small cams on the main closing cam shaft will
mechanically open the two contacts independently and the torque brake will stop its
rotation.
If, when the protector closed, a primary feeder fault, or other conditions should occur which
would cause sufficient power reversal to operate the network relay, tripping of the protector
will occur as follows:
1. The network relay will close its tripping contacts, thus completing a circuit through
the trip coil and series “a” switch.
2. The trip coil armature will then pick up (if the impressed voltage is 7-1/2 percent of
normal or over) and release the trip mechanism latch, allowing the breaker to open.