Our generator is connected to grid by 33kv line. Due to some reason we supply a fixed amount of power to grid. This is done by a device named Auto Load Limiter Device which looks like
It measures line current. But here we used this device to limit the power. We can set upper limit and lower limit of current. For example,
Upper limit=120A,
Lower limit=117A,
Then it reduces fuel when current is greater than 120A and vice versa for lower than 117A.
For a 33kv line 120A means around 6MW power.
But the problem is, there is no polarity check for power. I mean it shows 120A(6MW) when we supply to grid. But if 120A(-6MW) comes to generator (it also called reverse power) it doesn't change it's polarity. Suppose in a faulty condition current becomes -20A(-1MW), now it is desired to be 117-120A(6MW), but MT4W increases it to -120A(-6MW) from -20A (-1MW). But our generator trips around -40A (-2MW).
How to solve this problem?
Is there any setting in MT4W so that it can measure reverse current?
What parameters should i change in MT4W?
You can say to use power meter which needs ct pt to measure power. power measurement is not my problem. We use this MT4W device to limit the load we supply to grid at 6MW not to measure power. You can ask why i need to limit the load to exact 6MW. The answer is, due to poor condition of transmission line we shouldn't exceed 6MW. This is a 40MW gas turbine and we supply 6MW to national grid and remaining 34MW goes to domestic load.
Every power plant can run in pre selected load mode where you can select the load you want to supply. But it is only possible when you are solely connected to grid. But i can't use this feature because i am giving 34 MW (15-34MW, 34 is peak value) domestic load. In grid you can control your power. You can supply as much as you want, also can take from grid as much as you want. But the domestic load is beyond the control.After fulfilling the domestic load, i have to control the load to grid at 6MW (which is done by MT4W). I already read the MT4W datasheet and there is a setting to show display value from -1999 to 9999 that means also negative value. But how to activate? Or is there any other way to limit the load?
Best Answer
The MT4W appears to be a ammeter/voltmeter.
It is not intended to be operated as a power meter.
It is not intended to be used for reverse power protection.
This function would normally be implemented on a protection relay. You should check your existing protection relays to see if they have a power / reverse power element already. If not, you will need some new equipment.
The SEL-751A is an example of a relay including directional power elements (ANSI 32). Budgetary price for this relay is $950 USD so it need not be expensive.
You will require both current and voltage inputs. This means you will need to install VT's if you don't already have them.
Detailed design and installation of this equipment should be done by people who are trained, deemed competent, and authorised to design and work with HV equipment in your country.