On Load Tap Changer

dear ,

Answer lies in your query sir.

AVR - means Auto matic Voltage regulator.

OLTC - means On load Tap changing device.

Both together, from HT side , i.e. receiving side of the supply, thay control ( regulate ) the set voltage . without switching off the supply, as control is on - ON load.

You will be setting the set volt of AVR to 405 V.

Dear Rooney,

1250kva 11/0.433kv transformer is quite definitely without on load tap changer.More likely it is equiped with off load tap changer with 5 or 7 steps of + - 2.5% with zero tappping at the middle.e.g +5%,+2.5%,0%,-2.5%,-5%.On load tap changer with OVR on 11kv will cost several times more than the transformer itself.However I may be wrong.

415v is your normal operating voltage when there is some load ( even with 60% of installed capacity) in the plant which has motors,etc installed to operate at 415v.To operate at 405v will cause your motors to draw more current and consume the same energy.Your resistive load such as heaters will consume less energy but will reduce heat output and will take longer time to reach the set temperature thereby consume the same as with 415v ultimately.405v is not a good idea and does not save energy.

1kv voltage drop out of 11kv nominal voltage supplied by the power supplyer is 9%.I suggest you buy a 750kva (60% of 1250) transformer with a off load tap changer that has a range of +5% and -10%.

Regards,

Khor

Normal voltage for the transformer is 433V and for certain country is 400V and when the transformer is loaded with load the voltage will drop to 415V. This is a standard voltage for a 433 V transformer.

By reducing the voltage from 415V to 405V will not and it does not help you to save energy.

The formula for the power in polyphase system is Power = VI √3 cos Φ. Power will remain the same. When you reduce the voltage, the current will increase and of course by reducing the voltage of the transformer will cause secondary effect to your equipment and process.

The On Load Tap Changer or sometime we call it OLTC, you can set the reference primary voltage of your incoming power supply. The AVR - means Automatic Voltage regulator will monitor the incoming primary voltage and if the primary voltage increase or decrease at certain percentage, the OLTC will automatically changes the transformer Tap to one step higher or one step lower without switching "OFF" the primary power supply. The OLTC will change the voltage Tap with the power supply "ON" and that why, we call it OLTC.

You have to study other method in order to save energy for your plant like example, by reducing the numbers of pumps operation when the plant is not in operation, reduce the number of air cond in the office, and reduce the numbers of sport light inside the plant during day time and e.t.c.

Correct me if iam wrong,

Normally energy saving by reducing voltage is applied in application like lighting only (There will be a little reduction in Lux compare to more reduction in power).

For motor application this concept does not work unless if the voltage is reduced by means of VFD (Voltage reduction with respect to frequency)

Energy saving is not by reducing the voltage or the current. If the voltage is reduce, the current will increase in order to maintain the power (Watt).

Let me show some example to you. Either it is apply to lighting or motors it will be the same.

Example if you have a 40 Watt Lighting that operate in 240V, then your current consumption for the 40 Watt lighting will be 166.667 mA.

If the voltage reduce to 220V but with the same 40 watt lighting, your current for the 40 Watt lighting will be 40 Watt/220V = 181.81 mA

That is the increase of 15.14 mA. See what I mean

Energy saving is that you replace the 40 Watt lighting with some lower watt lighting (which is lower than 40 watt) but with the same Lux output.

For motors application, bear in mind that not every motor can save energy by using the VFD. It all depend upon the application of the motors and the load it connected to. Some application can reduce the motor speed and power and some application cannot.

Instead of running the motor at 100% power, you can control your motor and run at 80% of the total motor full power. Thus, you have some saving about 20%. then again you have to see if the 80% of the motor full power is capable to run your equipment.

Energy saving need to study in depth, in all aspect and impact to the operation and process and not just reducing the current or voltage only.