3 phase motor emergency stop

Thread Starter

Nstevens

Joined Oct 13, 2021
1
Hey, I am working on a project that requires a 3 phase AC motor using a speed controller that has a 1 phase input and a 3 phase output. I am trying to wire an emergency button that will stop it immediately or quickly as possible. Do yall have any suggestions on parts or wiring diagrams? thanks.
 

MaxHeadRoom

Joined Jul 18, 2013
25,977
A typical NAND hard wired E-stop circuit is the norm, and mandated by NFPA79 etc.
Sounds like a VFD controller, In N.A. and much of Europe there are 3 situations that can apply to an E-Stop.
For imediate stop, a Relay or contactor on the 1ph input is required with suitably placed E-stop P.B.'s are placed at strategic positions for operator operation, together with such as M/C over travel L.S's or similar etc conditions wired into the NAND operated E-Stop relay string in order to remove power to the E-stop contactor/relay..
Also see the Schneider link here https://forum.allaboutcircuits.com/threads/3-phase-motor-using-relays.182441/
 

strantor

Joined Oct 3, 2010
6,112
Many (most?) modern VFDs have a pair of STO (Safe Torque Off) inputs, sometimes called "base block" which gives a more immediate stop of output power than opening a contactor on the VFD input. These inputs seem to satisfy most international safety regulations but I think those regulations are a bit short-sighted. What they don't stop is a spinning motor. Half of the function of a VFD is to slow a motor that might have a lot of inertia. Depending on the application (please excuse my use of free thought) it may be safer NOT to use these inputs, or a contactor, but instead use the VFD in its normal mode to initiate a rapid deceleration. Yes, mechanical brakes can be employed for emergency situations, but I'm sure the guy getting wrapped around a spindle head first would appreciate any help the machine designer could offer to assist the mechanical brakes.
 

Techohead

Joined Nov 23, 2020
11
Applying DC across 2 of the motor wires for a short time will bring it to a quick stop. I once worked on a device that used an SCR with an adjustable phase control to adjust the breaking force, with a timer and freewheel diode. I don't remember what brand it was, but it was probably ASEA or one of those manufacturers of motor speed controls. VVVF drives need to have dynamic breaking or regenerative breaking capability to stop it quickly.
 

strantor

Joined Oct 3, 2010
6,112
Applying DC across 2 of the motor wires for a short time will bring it to a quick stop. I once worked on a device that used an SCR with an adjustable phase control to adjust the breaking force, with a timer and freewheel diode. I don't remember what brand it was, but it was probably ASEA or one of those manufacturers of motor speed controls. VVVF drives need to have dynamic breaking or regenerative breaking capability to stop it quickly.
This is called DC injection braking and is a pretty standard feature on most VFDs nowdays. No need to make a special circuit for it.
 

MaxHeadRoom

Joined Jul 18, 2013
25,977
The way to do it if concerned about breaking the power input connection, (although I have never had a problem)!, is to issue a Soft stop (input) to the VFD and then disconnect the power.
But to obey the NFPA rules the input supply must be disconnected at some point during an E-Stop.
 
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