Isolation contactor on VFD 1

[greta]

I'm designing a machine for the US market.
Is it mandatory an IC in case of E-stops?
I've seen several E-stop circuits relying just on a digital input of the VFD. Is this allowed by the norms ?
My E-stop is a controlled stop so the IC - if needed - will drop just once the motor is standstill.
If IC needed, to be installed on the VFD input od output side?

 

[dpc]

It may depend on the application - some uses, such as elevators have special code requirements. But in general, I do not think that an emergency stop shutdown requires the use of an isolation contactor.

However, using a controlled shutdown for E-stop is very unusual, at least in my experience. In all applications I have been involved in, the Emergency Stop was an immediate shutdown. Unless this is more dangerous (to people) than the controlled shutdown, the emergency shutdown should be immediate.

Another option I have seen used is to shunt trip the breaker that serves the VFD on emergency stop. This has the advantage of forcing a manual reset prior to re-starting, although there are other ways to accomplish this.

Hope this helps.

 

[TheDOG]

A contactor on the input of the drive will not serve as an emergency stop.
Depending on the loading of the motor, the bus capacitors may keep the bus voltage up to a level that will still provide power to the motor, after the input power is removed. If the load requires emergency stopping, you may still be able to use the drive to provide dynamic braking. In Australia for example, this complies with AS 4024.1 - 1996 (Safe guarding of machinery) - you will need to check with the local regulations.

 

[jbartos]

Suggestion: Also, the regenerative drives have capability of motor stopping. If not an immediate stop is required or motor load has enough power to stop the motor shaft quickly, then the E-stop could be on the PLC output that trips the starter, if applicable. There are various safety codes covering e-stops, e.g. NFPA-79, IEC, EN, etc.

http://www.nfpa.org

 

[bitoy]

You may configure your emergency stop to control both a contactor installed at the input and output of the VFD.This is to insure that the VFD and the motor are totally isolated from power.The VFD is normally run with load or load shall be connected first before command to the VFD to ramp is initiated and is controlled at the VFD digital input.

 

[jOmega]

Greta:

Emergency Stopping is defined by NFPA 79 Electrical Standard for Industrial Machinery.

Quoting from .... 9.6.3 Emergency stop.

".....the emergency stop has the following requirements:
— it shall override all other functions and operations in
all modes.
— power to the machine actuators that can cause a
hazardous condition(s) shall be removed as quickly as
possible without creating other hazards (e.g., by the
provision of mechanical means of stopping requiring,
no external power, by reverse current braking for a
Category 1 stop.
— reset shall not initiate a restart."

"The emergency stop shall function as either a Category 0
or a Category 1 stop. The choice of category of emergency
stop shall be determined in accordance with the
requirements of the application."

"Where a Category 0 stop is used for the emergency stop function, it shall have only handwired electromechanical components. In addition, its operation shall not depend on electronic logic (hardware or software) or the transmission of commands over a communications network or link."

"Where a Category 1 stop is used for the emergency stop function, final removal of power to the machine actuators shall be ensured and shall be by means of electromechanical components.

Category 1 & 2 stops are defined in 9.5.2 Stop Functions as follows:

— Category 0: stopping by immediate removal of power to
the machine actuators (i.e., an uncontrolled stop)
— Category 1: a controlled stop with power to the
machine actuators available to achieve the stop and
then removal of power when the stop is achieved.

In either case, the term actuators includes the drive and/or the motor; be it of the AC or DC type.

So, a mechanical means must be provided to remove the power.

It must be mechanical because electronic drives can fail in the ON state.

Hope this helps.

\

 

[jbartos]

Suggestion: In addition to the previous posting content, there are other requirements on e-stop, e.g. location, shape of button, etc. It may just pay off to become familiar with the NFPA 79.

 

[thinker]

Since one of the posts suggested the usage of the contactor
on VFD output, one important issue should be considered:
make sure that contactor arc suppression system will be able
to function at very low frequency and full load.

 

[jOmega]

Thinker:

You raise a viable issue. Perhaps you would enlighten us as to what a typical "arc suppression system" would be on an AC, HP rated contactor.

Also, please consider that when applied to a VFD, the contactor can be used to interrupt the flow of INPUT power to the VFD instead of interrupting the output of the VFD to the motor... The intent is to remove the source of power from the motor. Interrupting the input power will accomplish that albeit with a slightly longer elapse of time until power is removed from the motor than would be the case with the contactor in the output of the VFD.

And last, consider that an Emergency Stop should not be used instead of a normal stop. It should be reserved for those occassions when life and limb are endangered. If the VFD or the contacctor, or any part of the machine is damaged in the process, then so be it. Is not the objective, after all, to minimized the threat to life and limb ?

Some would argue that it should also be used when the machine is in jeopardy. In such case, the initiation of an Emergency Stop should be a conscious decision with due consideration to the fact that additional equipment damage may result from the invocation thereof.