Attached drawings of an AC Dynamic Lowering Hoist Control, used on a Hoist with a Wound Rotor AC Induction Motor.
Schematics of complete system and close-up details are included.
Also included are text notes for this system and text notes regarding Wound Rotor Motors, which was submitted to be by an ECN member.
It was quite some time ago and I cannot remember the member and when this was submitted to me. If that member would send me a message I would give credits.
Also, I'll try to setup a discussion thread for this topic in the Electrical Theory area.
Here's the drawings!
Fig. 1-1: Overview of the complete system schematic wiring diagram for AC Dynamic Lowering Hoist Control.
Fig. 1-2: Detail of the Disconnect and Directional contacts sections.
Fig.1-3: Detail of the control circuit, DC power supply and mechanical brake sections.
Fig. 1-4: Detail of the Wound Rotor Motor.
Fig. 1-5: Detail of the Secondary Resistors network, time-delays and Dynamic brake systems.
Fig. 1-6: Detail of Resistor network and Motor as connected.
Fig. 1-7: Description and detail of collector bar and collector shoe
Text For This System;AC Dynamic Lowering Hoist Control
A typical AC Dynamic lowering Hoist control power circuit with Rectifier-operated DC shunt Magnetic brake and power limit switch is shown in this Schematic.
The Motor, brake, and limit switch are mounted on the Trolley. The brake relay BR
and the Rectifier are mounted on the control panel.
Such an arrangement requires 10 collector rails, as shown.
In hoisting, contactors H
and the brake relay BR
close on the first point of the master switch to release the brake and apply hoisting power to the motor with all secondary resistance in the circuit.
On the second point, 1A
closes without delay; and on the third, fourth, and fifth points, 2A, 3A
, respectively, close in sequence under control of relays responsive to variation in Rotor Frequency or motor speed.
On entering the limit switch, the two normally closed contacts LS
open to remove power from the motor and to permit the brake to set.
On the first point lower, contactors L, DB
close, tying motor terminals T1
together and applying single phase voltage across T2
. The brake is also released, allowing the load to lower (if Overhauling) against Dynamic braking or retarding torque developed by the motor as it gains speed. The closure of 1A
gives a secondary resistance value which provides a retarding torque of approximately full-load torque at synchronous speed.
On the point lower, DB
opens and M
closes to apply balanced 3-phase lowering power to the motor, and at the same time 1A
opens to provide low torque. This point is used in "Inching" a light load downward.
If the master switch is held on the second point, 2A, 3A
will close in frequency-controlled sequence.
If the master switch is moved to the third point from the "Off" position, 1A
closes instantly to provide higher driving torque in the lowering direction, and 2A, 3A
follow in frequency-controlled sequence.
With the secondary resistance short circuited, and with an overhauling load, the motor runs at a speed somewhat in excess of synchronous speed, the speed being limited by regenerative braking.
On returning the master switch to the second point, 1A
opens without any effect, but when the master switch is returned to the first point, M
opens and DB
close, while 2A, 3A
open to set up the Dynamic braking connections.
If the master switch is then moved to the "Off" point, DB, L
remain closed and the brake sets. Dynamic braking assists the brake in bringing the motor to rest, at which time one of the frequency-responsive relays 2AR
opens its contacts to open L, DB
This is reffered to as "Off Point Dynamic Braking".
The retention of Dynamic braking during the setting time of the magnetic brake prevents the load from dropping during this short time interval and greatly reduces brake-lining wear.
-----end of notes text-----
FYI: I'll try to insert speed-torque curves of a Dynamic braking AC Hoist controller built in accordance with the wiring diagram / Schematic shown here, once I compile the data and make it a Raster Image.
S.E.T. 10/13/2002 - C:\Pc2\website\images\gif\hoist_text.txt no rev.
end. new as of 10.17.2002 by S.E.T.
editted to add text! DOHHHH!!!
[This message has been edited by Scott35 (edited 10-18-2002).]