General information
On-load tap-changer devices of the RNTA type for a rated voltage of 35-60 kV, rated currents of 125, 200-630 A are designed for built-in step-by-step voltage regulation of three-phase general purpose power transformers under load with regulation in the neutral.
RNTA devices are manufactured in various designs depending on the rated current, rated voltage, number of stages, and control circuit.
RNTA devices are designed to operate in transformer oil at oil temperatures from 100° C to minus 25° C, as well as up to minus 60° C without switching.
Ambient air temperature from +40° C to -60° C (climatic modification U1 and HL1).
The main technical data of RNTA devices are given in Table 1.
| Parameter name | Device name | ||
| RNTA-35/125 | RNTA-35/200/400/630 | RNTA-60/200/400/630 | |
| Rated voltage, kV | 35 | 35 | 60 |
| Rated current, A | 125 | 200/400/630 | 200/400/630 |
| Rated voltage of the stage, kV | 0.5 | 2.5/1.75/1.3 | 2.5/1.75/1.3 |
| Number of control stages | 8 | 16; 18 | 16; 18 |
| Mechanical wear resistance, thousand shifts | 1500 | 500 | 500 |
| Electrical wear resistance, thousand switching cycles | 750 | 400/250/120 | 400/250/120 |
| Value of steady-state TKZ, kA eff | 2.5 | 4 /6 /8 | 4 /6 /8 |
| Test impulse voltage, kV: | |||
| between zero point contacts and ground; | 200 | 200 | 270 |
| between contacts of the same phase (range); | 95 | 220 | 220 |
| between adjacent contacts (stage); | 50 | 65 | 65 |
| between contacts of different phases | 120 | 270 | 270 |
| Oil change frequency, thousand shifts | 100 | 50 | 50 |
| Switching time to one position, s | 0.6 | 3 | 3 |
| Drive unit | specialist. | PDP-5 | PDP-5 |
| Year of development | 1985 | 1994 | 1999 |
Design
On-load tap-changer devices type RNTA of submersible design are built into the transformer tank.
Depending on the type of RNTA device, they are made of a contactor and selector or on the principle of a load switch, i.e. the functions of the selector and contactor are combined in one switching mechanism (RNTA-35/125).
The devices are controlled by a drive or a control cabinet (for RNTA-35/125). Devices, as a rule, operate in automatic mode from an automatic control unit.
The following are supplied complete with on-load tap-changers:
- automatic control unit (voltage regulator), which provides a command to turn on the on-load tap-changer. The voltage regulator operates automatically when the voltage at the transformer terminals changes;
- protective relay: gives a signal to turn off the transformer if the PU contactor is not operating correctly;
- The temperature sensor-relay interrupts the on-load tap-changer control circuit when the oil temperature is below minus 25° C.
The devices allow remote control and manual control from the handle when setting up or testing the transformer.
OLTC DEVICE TYPE RNTA-Y-35/125
OLTC DEVICE TYPE RNTA-Y-60/200, 400, 630
OLTC DEVICES TYPE RNTA 35/200-630
