Information

The various types of the OLTC produced by our company are different in the structure of the OLTC, the connection between the OLTC and the winding of transformer, the installation on the transformer and the mode of operation.

1. The structure of the OLTC

The main difference of the OLTCs is that the one consists of the diverter switch and the tap selector but the other is the selector switch. When the OLTC composed of diverter and selector is operated, the tap is selected by selector first and then switched by the diverter. In the selector switch this process is completed at the same time. The type C1 and SYXZ-110/200-7 are the OLTC composed of diverter and selector, the type F1, SYJZZ-35/200-7 and SYXZZ-10/100-9A are the selector switch.

According to the connection between the OLTC and the transformer three modes of connection are applied to the following: in the neutral point (Neutral), in the terminal of the winding (Terminal) and in the middle of the winding by bridging (Bridging). The Neutral is only applied to that the three windings are "Y"(star) connection. The neutral point of transformer is in the OLTC.The type C1, SYXZ-110/200-7, SYXZZ-10/100-9A and SYXZZ-35/200-8A are the Neutral. The Terminal and Bridging can be applied to "Y" or "D"(delta). The type SYJZZ-35/200-7 is the Bridging and the type SYTZZ-35/200-8 is the Terminal. The type F1 can be applied any one of three modes. The neutral point of the type F1, C1 and SYXZ-110/200-7 can be connected to the neutral bushing of the transformer,but the type SYXZZ-10/100-9A and SYXZZ-35/200-8 can't.

To extend the regulating range, the change-over selector can be added in some types of OLTC. These are type F1, C1, SYXZ-35/200-15 and SYXZ-35/200-27.The change-over selector of type F1, SYXZ-35/200-15 and SYXZ-35/200-27 can be applied to the connection of reversing switch and coarse tap selector, but the type C1 only to the connection of reversing switch.

The mode of operation is different in various type of OLTC. The type F1, C1 and SYXZ-110/200-7 are operated by the motor drive unit that is installed on the wall of tank of transformer but the type SYXZZ-10/100-9A and SYJZZ-35/200-7 by the OLTC controller that is mounted on the switchboard in the control room with a cable.

The processes of a tap changing in the OLTC consisted of diverter switch and tap selector (only 1 pole):

Fig.1 Show the OLTC's switching from tap position 3 to 4

(from left to right, R is transition resistance)

The processes of a tap changing in the selector switch (only 1 pole):

Fig.2 Show the selector switch's switching from tap position 3 to 4

(from left to right, R is transition resistance)

The processes of a tap changing in the Bridging selector switch (only 1 pole):

Fig.3 Show the Bridging selector switch's switching from tap position 3 to 4

(from left to right, R is transition resistance)

2. The connection between the OLTC and the winding of transformer

The connections of Star and Delta in the OLTC:

Star in Neutral Delta in Terminal Delta in Bridging (without neutral terminal)

Star in Neutral Star in Terminal Star in Bridging (with neutral terminal) (in middle of winding)

Fig.4 The connections of Star and Delta in the OLTC

Basic connections of the tap winding (only 1 pole):

a b c

a - Linear tap winding

b - Reversing switch connection

c - Coarse tap selector connection

Fig.5 Basic connections of the tap winding

3.　The installation on the transformer

There are two ways about the installation of OLTC on the transformer. One is on the standard type tank and other is on the bell type tank.

On the top of standard type tank a hole is cut and the OLTC is mounted, then the winding is connected to the terminals of the OLTC.

On the bell type tank a hole is cut also, but the OLTC is placed a supporter on the core and winding assembly,then the winding is connected to the terminals of the OLTC and the bell type tank is installed.The connection of oil between the OLTC and the transformer is cut off with seal finally.

The type F1, C1 and SYXZZ-110/200-7 can be applied to the standard and bell type tank of transformer, but there are differences. The placing on the supporter of type F1, C1 is temporary and the cutting of connection of oil is by the replacing the OLTC head that is separated from the OLTC in the installing process. The placing on the supporter of type SYXZZ-110/200-7 is screwed and the cutting of connection of oil is with the eccentric flange and the seal gasket.

The type SYXZZ-10/100-9A and SYJZZ-35/200-7 can be applied to the standard type tank of transformer only.

An accessory of the OLTC operated by the motor drive unit is the bevel gearing.The bevel gearing is mounted on the tank of transformer, a vertical shaft is connected between the bevel gearing and the motor drive unit and a horizontal shaft is between the OLTC and the bevel gearing. The horizontal shaft is mounted on the top of OLTC for the type F1, C1 but on the middle for the type SYXZZ-110/200-7. The material of the horizontal shaft is metal for the type F1,C1 but insulation for the type SYXZZ-110/200-7.

4. The mode of operation

The OLTC of the type F1,C1, and SYXZ-110/200-7 are operated by the Motor Drive Unit. The motor, the transmission gear, the control gear, the control electrical equipments, the tap position indicator and transmitter, the operation counter are mounted in the housing. The torque is transferred from the top of the motor drive unit into the OLTC through the vertical shaft, the bevel gearing and the horizontal shaft. The tap position transmitter in the motor drive unit is connected to the Tapping Positions Indicator mounted in the control room by the cable. The push buttons can be connected to the control room too.

The OLTC of the type SYXZZ-10/100-9A and SYJZZ-35/200-7 are operated by the OLTC Controller. The motor, the transmission gear and the tap position transmitter are mounted in the oil cylinder of the OLTC. A control cable is connected between the OLTC and the Controller. The push buttons, digital display elements, relays and operation counter are installed in the controller. There are two controllers: with or without automat. The controller with automat is applied to the power transformer to stabilize the voltage output but the other to the industrial transformer.

5. Some of examples