Voltage transformers. (A) The primary winding of VTs must be connected to the circuits being measured.
Voltage transformers. 15- Routine tests ▪ Verification of terminal markings. ▪ Power- frequency voltage withstand test on the primary terminals. ▪ Partial discharge measurements. ▪ Power-frequency voltage withstand test on secondary terminals. ▪ Power – frequency voltage withstand test between sections. ▪ Determinations of errors (accuracy test for phase angle and ratio errors). ▪ Measurement of primary and secondary winding resistance. ▪ Pressure test for the enclosure. ▪ Enclosure tightness test at ambient temperature. 16- Type tests
Voltage transformers. Two VTs or one VT with two or more secondary winding sets in accordance with IEC Standard 186 and with a minimum standard of accuracy class 0.2 shall be provided. The VT secondary winding supplying the main Meters shall be dedicated to that purpose. The VT used for secondary winding supplying the check Meter may be used for other purposes provided the overall accuracy requirements in Section 4.2.1 are met and evidence of the value of the additional burden is available for inspection by Scottish Settlements. The additional burden shall not be modified without prior notification to Scottish Settlements, and evidence of the value of the modified additional burden shall be available for inspection by Scottish Settlements. A VT test certificate(s) showing errors at the overall working burden(s) or at burdens which enable the working burden errors to be calculated shall be available for inspection by Scottish Settlements. The total burden on each secondary winding of a VT shall not exceed the rated burden of such secondary winding. Separately fused VT supplies shall be provided for each of the following:-
Voltage transformers. A dedicated voltage transformer secondary winding in accordance with IEC Standard 186 and with a minimum standard of accuracy to Class 0.5 shall be provided for the sole use of metering of a circuit for Allocation purposes. No other burden shall be connected to this dedicated winding. The main Meter shall always be connected to this dedicated winding. The check Meter may also be connected to this dedicated secondary winding. Alternatively the check Meter may be connected to another secondary winding which shall be in accordance with IEC Standard 186 and with a minimum standard of accuracy to Class 0.5. Other burdens may be connected to this other secondary winding provided that Scottish Settlements is notified and the overall accuracy requirements in Section 4.2.1 are met and evidence of the value of the additional burden is available for inspection by Scottish Settlements. The additional burden shall not be modified without prior notification to Scottish Settlements, and evidence of the value of the modified additional burden shall be available for inspection by Scottish Settlements. A VT test certificate(s) showing errors at the overall working burden(s) or at burdens which enable the working burden errors to be calculated shall be available for inspection by Scottish Settlements. The total burden on each secondary winding of a VT shall not exceed the rated burden of such secondary winding. The VT supplies shall be fused as close as practicable to the VT, with a set of isolating links, suitably identified, provided locally to the Metering Equipment. Superseded
Voltage transformers. A single VT secondary winding in accordance with IEC Standard 186 and with a minimum standard of accuracy to Class 1 shall be provided for the main Meters and check Meters of a circuit. The voltage transformer secondary winding may be used for other purposes provided the overall accuracy requirements in Section 4.2.1 are met and evidence of the value of the additional burden is available for inspection by Scottish Settlements. The additional burden shall not be modified without prior notification to Scottish Settlements, and evidence of the value of the modified additional burden shall be available for inspection by Scottish Settlements. A VT test certificate(s) showing errors at the overall working burden(s) or at burdens which enable the working burden errors to be calculated shall be available for inspection by Scottish Settlements. The total burden on each secondary winding of a VT shall not exceed the rated burden of such secondary winding. The VT supplies shall be fused as close as practicable to the VT, with a set of isolating links, suitably identified, provided locally to the Metering Equipment.
Voltage transformers. A single voltage transformer secondary winding in accordance with IEC Standard 186 and with a minimum standard of accuracy class 1 shall be provided for the main and check metering of a circuit. The voltage transformer may be used for other purposes provided the overall accuracy requirements in clause 4.2.1 are met and evidence of the value of the additional burden is available for inspection by the SSA or its Agent. The additional burden shall not be modified without prior notification to the SSA, and evidence of the value of the modified additional burden shall be available for inspection by the SSA or its Agent.
Voltage transformers. All voltage transformers shall be checked for polarity, phasing and secondary output. All electromagnetic type voltage transformers shall have insulation tests carried out on them at 500 Volts to earth and between windings.
Voltage transformers. For 220 kV and 60 kV levels, inductive or capacitive transformers will be provided, and for medium voltage they will always be the inductive type. Take into account that transformers should not produce ferroresonance effects associated with the capabilities of the aerial lines. All metal parts will be hot dip galvanized according to ASTM or VDE Standards, and the windings will be made of copper, insulated with oil impregnated paper, as appropriate. Transformers will be designed to withstand thermal and mechanical stresses due to short circuits on the secondary terminals during one-second periods with full voltage maintained on the primary. Transformers shall not show visible damage and will continue to meet the requirements of this specification. Temperature on the copper windings must not exceed 250 ° C under these short circuit conditions (for an initial condition of 95° C at the hottest point). The capacitive divider elements for 220 and 60 kVtransformers containedin brown porcelain insulators form a self-supporting column. Capacitive divider coils will be made of aluminum sheet with impregnated paper insulation or polyester film and anti-inductive type to improve transient response. Reactance may be isolated in oil, in air or SF6 gas. Voltage transformers shall have the following main features: Description Type of Installation 220 kV Outdoors 60 kV Outdoors MT kV Indoors Secondary voltage 110/√3 V 110/√3 V 110/√3 V Measuring core characteristics
Voltage transformers. For the 220 kV levels, capacitive transformers shall be provided, according to the application. It must be taken into account that the transformers shall not produce ferro resonance effects associated with the overhead line capacities. Voltage transformers shall have the following main characteristics: Description 220 kV Type of insulation Outside Secondary voltage 110/√3 V Characteristic of measurement cores a) Accuracy class b) Power 0,2 % 15 VA Characteristics of protection cores a) Accuracy class b) Power 3P 15VA
