Soft Start and VFD with bypass

I go along with Gil. The cost of 100% reliabilty is very high.

I think risk and consequence of failure must be taken into account. Two arbitrary examples:
If this is a 100HP circ pump in a production facility I am sure no one will get hurt if it fails. OK you dont produce for a day or so and you may lose raw material (food facility)
On other hand if this is a 10 HP unit that pumps oxygen to patients in a hospital then cost may be justified. If unit fails you have dead people.

Gil is also correct how are you going to completely deenergize a unit that is connected in parallel with another energized one? In this case I would consider using manual disconnects to switch out the VFD and switch in the DOL starter. They could also be locked out which I am sure a servicing electrician would find as a relief. Would require 4 disconnects.

You would ideally need two different enclosures to ensure electrician is not working hot.

FINALLY IF DOL is added the conductor from the power supply must be upsized.
Reason
on a VFD you can size wire much smaller than you need to size it with DOL. Example for 100 HP unit at 480 volt, full load amps about 100.
On a VFD setup you would only need 100 amp conductor
on a DOL you would need 300 amp capacity from source to the starter relay (old days was 300% now you go thru a couple charts in NEC with different results but 300% is easier for example here).
From contactor on you would only need 100 amp conductor unless a long run then I would apply larger conductor. Even on a short run I still use larger wire - cheap compared to burning out motor due to undervolage on start.

You would also need overload sensors sized for 100 amp.

I would seriously consider buying a spare VFD unless you need 100% reliabilty (life safety critical) but to assure 100% you have to have two completely independent units including pump etc etc (just like Gil recommended). This would probably cost just as much and would give more reliability.

Dan Bentler
 
I didn't intend for this to become a discussion on the validity of bypasses integrated or otherwise. The customer wants a bypass of some sort. So far we have used the external bypass route, but we're trying to look at other options like bypass that is integrated, and has "true bypass" so the pump can be started even in the event of a soft start failure, and with the flick of a switch.

Gil47, your point is well taken, but sometimes the customer wants what they want, and it's our job to give it to them.
 
I didn't intend for this to become a discussion on the validity of bypasses integrated or otherwise.


Sorry but that's not how it works..... You may get lots of information you don't need...or don't THINK you need..... just disregard it. Somebody ELSE may find it useful. Heck, we may all end up drinking beer on page 8. I've seen it happen.

THENNNnnn... when you burn something up because you didn't listen.......WWWEEEeeee get to say "I told you so". lol

You want to talk about bypass??? We may want to talk about the extra inrush current associated with DOL starting.... There's a valid connection. The power company where I am frowns on starting any motor greater than 75hp DOL. They don't want the lights to dim all over the neighborhood when the local golf course fires off the irrigation cycle....... SSSOOOoooo since "bypass" equals "DOL", it's not unreasonable for someone here to bring up increased amps and inrush when YOU bring up BYPASS.

By the way, when we all ended up on page 8 drinking beer and "posting under the influence" we hadn't heard from the OP for about 5 pages.

:D

Stationmaster
 
Sorry but that's not how it works..... You may get lots of information you don't need...or don't THINK you need..... just disregard it. Somebody ELSE may find it useful. Heck, we may all end up drinking beer on page 8. I've seen it happen.

THENNNnnn... when you burn something up because you didn't listen.......WWWEEEeeee get to say "I told you so". lol

You want to talk about bypass??? We may want to talk about the extra inrush current associated with DOL starting.... There's a valid connection. The power company where I am frowns on starting any motor greater than 75hp DOL. They don't want the lights to dim all over the neighborhood when the local golf course fires off the irrigation cycle....... SSSOOOoooo since "bypass" equals "DOL", it's not unreasonable for someone here to bring up increased amps and inrush when YOU bring up BYPASS.

By the way, when we all ended up on page 8 drinking beer and "posting under the influence" we hadn't heard from the OP for about 5 pages.

:D

Stationmaster

OK. Here's the deal. The client is a water utility. When they want a pump on, they want a pump on. No questions, no "well you really shouldn't because of this, or that". I understand all of the points against having bypass, and thank you for providing useful information for people on this board.

Now... does anyone have a product they can recommend that addresses my original question? I can't seem to find a soft start with 'true' bypass built in.
 
The RAM unit will do it...

From the manual

Automatic Bypass:
The RAM DBS includes a horsepower rated bypass contactor that is automatically engaged after the motor has reached full speed or when the bypass delay has expired. This reduces power losses and heat build up in the enclosure and allows the starter to be operated continuously, fully loaded, in an unventilated enclosure, surrounded by 40 oC a-m-b-ient air without overheating. The bypass contactor can also serve as an emergency starting device.

 
I read this and say, all very well to make the bypass arrangement for the situation where you have a VFD or Soft start failure, along with a panel twice as big and you want one that is intergrated, now for the but.

You add the needed contactors and controls, overloads fuses, larger panel, and so on,
now you have a VFD or soft start that needs serviced.
Please explain how you remove it safely, from the jumble of added controls, and switch gear, as well as more points of failure, and then you need to find an Electrician that would confidently work on it without a full isolation.

In the very few occasions, we might have the need to run existing machinery when failure of Vfd or soft starter would be a problem, we have a convetional starter feed the VFD or Soft start, and by link wires swap the way its started after removing, then linking motor leads from VFD with the supply leads to the VFD.

If fast swap is required, I believe a back reserve pump or capacity of what ever, is the best, wisest, safest option.

Now did I mention cost of building this arrangement.

OK. Here's the deal. The client is a water utility. When they want a pump on, they want a pump on. No questions, no "well you really shouldn't because of this, or that". I understand all of the points against having bypass, and thank you for providing useful information for people on this board.

Now... does anyone have a product they can recommend that addresses my original question? I can't seem to find a soft start with 'true' bypass built in.

I do not think you will find what you want off the shelf.

As I see it you have 3 choices
1. Put in complete redundant units
2. Have factory build a custom VFD
3. Install controls such that you have a parallel DOL and VFD motor control setup.

I think also this may be a good time to tell the customer NO.
You just may not want to get involved in doing what they want.
Dan Bentler
 
Alos be aware that there is a big difference between the bypass contacts built into soft-starters and external bypass contactors. The contacts that are typically built it cannot handle the inrush loads associated with across the line starting. The SCRs handle the inrush current so the contacts are rated for the FLA of an already running motor but don't have the necessary margin for the inrush.
 
Now... does anyone have a product they can recommend that addresses my original question? I can't seem to find a soft start with 'true' bypass built in.

Nope. Your "original question" is inherently flawed. Explaining HOW would obviously be too much information.

Good Luck,

Stationmaster
 
This is an option that nearly meets what you appear to be asking, but does not meet exactly your requirements.

Wire up two totally independent starer systems, say one VFD and one DOL starter, then put a plug on the outputs of each starter, then on the motor cable put a plug that can be plugged into either one or other of the starters.
Now if this needs to be automated, fit two contactors with needed interlocking in place of the plugs.
I feel this will keep it relatively simple and reliable, while being easier to maintain, and might meet the customers requirements.
 
This is an option that nearly meets what you appear to be asking, but does not meet exactly your requirements.

Wire up two totally independent starer systems, say one VFD and one DOL starter, then put a plug on the outputs of each starter, then on the motor cable put a plug that can be plugged into either one or other of the starters.
Now if this needs to be automated, fit two contactors with needed interlocking in place of the plugs.
I feel this will keep it relatively simple and reliable, while being easier to maintain, and might meet the customers requirements.

I should have thought of using plugs. Even better than disconnnects - provided motor current is 30 amp or less it should be less expensive than disconnects, and will provide complete isolation from unit being serviced / repaired.

If motor current (FLA) is over 100 amps it may not be competitive cost wise with disconnects.
Good un Gil

Dan Bentler
 
You can use the drive or soft starter Digital output for this purpose
In all drive you can find one output for Drive Healthy(either fixed or programmable) you can use that contact output & through this contact you can start the bypass contactor either DOL or star/delta whatever you like
So if Drive fails the motor will be bypassed through the contactor

Parag
 
OkiePC has already given one source for a softstart with start-duty bypass. Benshaw in Glenshaw PA also makes softstarts with bypass but you must specify START-DUTY. The standard duty bypass is RUN-DUTY only. But it is available.

As to drives or VFD's, unless you actually want variable speed, a VFD will always cost you more. But, as mentioned earlier, most manufacturers that build drives for the HVAC field, also have an integrated start-duty bypass option.

So, it looks to be like you can choose either, or, Bosko.
 
I have never seen a VSD/soft starter with a bypass as you describe. The only bypass I have seen is once the motor is running.
The only 'bypass' situation I have seen in VSDs is in ones that have a 'fire' input. In other words no protection - crash and burn - run till the whole thing dies. I do not know if it is really a bypass though - I suspect that if the thyristors die then the whole thing dies.
 

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