elevmike
Member
I have a customer who has standby power via emg generator for his building. The emg generator is suppooosed to be sized to operate the hvac system, lighting, and one of the two elevators. The problem is that when the elevator starts the generator bogs down and the elevator pump motor cant get up to speed thus letting the resident smoke out of the motor due to a severe lack of CEMF etc..
Get this..The generator contractor says itās a problem with the elevator because everything else works properly, and the KW rating on the generator matches all of the collective demand. ??? I tried to explain to the customer the technical aspects of locked rotor current, and starting current, frequency shifts etc.. etc.. I told him that we should run a test on the generator to watch the frequency on a scope, and current shift when the elevator pump motor is starting under full load conditions. ( I figured if the generator is sized right, it may be a problem with the governor on the generator not properly reacting to the load). So the customer told the generator contractor what I said. The generator contractor went to the site, started the generator, and pointed to the Hz meter that read 60 Hz, then to the tag that showed the proper KW rating for the pump motor FLA. (we were not invited to this little ceremony). He then told the customer that he should have us install a soft start on the elevator so that we can control the starting current ramp. I again tried to explain to the customer again that the generator must be sized to accommodate the collective starting currents of all inductive loads. However my powers of persuasion are not as strong as the generator contractors. (lowest bid gets the job), and the generator guy convinced the customer that we must install the soft start to resolve the issue.
I told the customer that I will not guarantee that the soft start will solve the problem. The customer responded by issuing me a P.O. for the soft start. ??? banghead
OK so I cant talk myself out of this job and must accept my fate to sell something to somebody that may have no redeeming value.
So now my problem is this: When I install the soft starter, since there is only one set of settings, the motor starting current ramp must be set to the lowest common denominator (the generator). I know that the customer will not be able to tolerate the long starting time when the elevator is on normal power.
To get around this problem I see one of two choices: 1) to install an AC drive that I can vary the ramp time based on the power supply (via analog signal from a plc, or digital drive), or 2) Install two soft starts, one to run the pump motor under normal power, and the other to run the pump under generator power. To me either choice is unacceptable. We are dealing with a 50 hp motor @ 240vac, so either one would be really expensive.
Do you know of a soft start that has two settings that would provide two different starting ramps on two different start/run inputs? Or am I all wet? What to do??
Thanks, Mike.
Get this..The generator contractor says itās a problem with the elevator because everything else works properly, and the KW rating on the generator matches all of the collective demand. ??? I tried to explain to the customer the technical aspects of locked rotor current, and starting current, frequency shifts etc.. etc.. I told him that we should run a test on the generator to watch the frequency on a scope, and current shift when the elevator pump motor is starting under full load conditions. ( I figured if the generator is sized right, it may be a problem with the governor on the generator not properly reacting to the load). So the customer told the generator contractor what I said. The generator contractor went to the site, started the generator, and pointed to the Hz meter that read 60 Hz, then to the tag that showed the proper KW rating for the pump motor FLA. (we were not invited to this little ceremony). He then told the customer that he should have us install a soft start on the elevator so that we can control the starting current ramp. I again tried to explain to the customer again that the generator must be sized to accommodate the collective starting currents of all inductive loads. However my powers of persuasion are not as strong as the generator contractors. (lowest bid gets the job), and the generator guy convinced the customer that we must install the soft start to resolve the issue.
I told the customer that I will not guarantee that the soft start will solve the problem. The customer responded by issuing me a P.O. for the soft start. ??? banghead
OK so I cant talk myself out of this job and must accept my fate to sell something to somebody that may have no redeeming value.
So now my problem is this: When I install the soft starter, since there is only one set of settings, the motor starting current ramp must be set to the lowest common denominator (the generator). I know that the customer will not be able to tolerate the long starting time when the elevator is on normal power.
To get around this problem I see one of two choices: 1) to install an AC drive that I can vary the ramp time based on the power supply (via analog signal from a plc, or digital drive), or 2) Install two soft starts, one to run the pump motor under normal power, and the other to run the pump under generator power. To me either choice is unacceptable. We are dealing with a 50 hp motor @ 240vac, so either one would be really expensive.
Do you know of a soft start that has two settings that would provide two different starting ramps on two different start/run inputs? Or am I all wet? What to do??
Thanks, Mike.