Synchronous motor used to support lowering of vertical gate.
Synchronous motor used to support lowering of vertical gate.
(OP)
I have a vertical gate that is raised by a synchronous motor via a gear box. Once the vertical gate is fully open a brake is engaged to hold the gate in the open position. To lower the gate the brake is released and a resistor load bank is used to absorb the reverse emf that is generated when the gate is being lowered.
Will this still work if normal power is lost to the synchronous motor? For instance, If normal power is lost and the vertical gate needs to be lowered, we can manually release the brake and connect the resistor load bank to the motor, Will the vertical gate fall on its own or will the torque from the synchronous motor help coast the gate down gracefully?
Any thoughts would be appreciated.
Thanks,
Will this still work if normal power is lost to the synchronous motor? For instance, If normal power is lost and the vertical gate needs to be lowered, we can manually release the brake and connect the resistor load bank to the motor, Will the vertical gate fall on its own or will the torque from the synchronous motor help coast the gate down gracefully?
Any thoughts would be appreciated.
Thanks,





RE: Synchronous motor used to support lowering of vertical gate.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor used to support lowering of vertical gate.
You need the field energized as well as the resistor bank connected before the motor will provide regenerative braking.
You maybe able to cobble something together with batteries on an old, slip ring motor, but with a new motor with a brushless exciter, you will have to energize the motor normally before the field will be energized.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous motor used to support lowering of vertical gate.
RE: Synchronous motor used to support lowering of vertical gate.
Are you gonna volunteer to stand under the gate while it is braked by residual magnetism?
Slightly more seriously, if there is any likelihood of a safety hazard arising because this gate may come down under a power fail condition then you need to seriously think about at a proper magnetic hold-off brake or equivalent.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor used to support lowering of vertical gate.
So, the next question is - exactly what type of synchronous motor is this?
RE: Synchronous motor used to support lowering of vertical gate.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor used to support lowering of vertical gate.
Thanks,
RE: Synchronous motor used to support lowering of vertical gate.
If I understand this right, when lowering, the gate acts as the prime mover driving the motor as a generator. The resistors are used to load the "generator" and thereby control the lowering of the gate. If this is excited by an external source through brushes you will need to have a battery back-up or stand-by generator (as waross suggested) so that you can excite the fields prior to manually releasing the brake.
Thanks
RE: Synchronous motor used to support lowering of vertical gate.
RE: Synchronous motor used to support lowering of vertical gate.
Any synchronous machine with a wound rotor (i.e. not a permanent magnet machine) will behave as I described: if you excite the field it will generate when it rotates. If you connect the terminals to a resistor bank it will act to brake the motor.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor used to support lowering of vertical gate.
A brush motor would be more likely since it will generate at low speed. A brushless could work too though once it picks up some speed.
But the use of resistors seems odd when the motor could just be line connected so it lowers at the same speed as when the gate is raised. So, knowing what type of motor and how the rest of the controls are working might give some clue as to why resistors are being used.
I was first thinking maybe the motor will overspeed and can't be synchronized when lowering but the motor should just run to sync speed plus the slip and then synchronize.
RE: Synchronous motor used to support lowering of vertical gate.
If that is so, a permanent magnet rotor is the most likely motor type (we do our guessing while Ricky keeps the secret from us).
If it is a PM motor, the resistors will work regardless of grid or not. The only thing that has to be considered is that the resistors are connected to the motor via NC contacts so that there will always be a path when power is off.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Synchronous motor used to support lowering of vertical gate.
.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Synchronous motor used to support lowering of vertical gate.
Again, thanks for all your comments.