Design Guide of the Medium Voltage Transformers for KACO Central Inverter

Transcription

1 Design Guide of the Medium Voltage Transformers for KACO This document describes the requirements of medium-voltage transformers that are connected to KACO central inverter. KACO new energy only accepts the warranty for medium-voltage transformers that have been installed following guideline provided in this application note. -NPD-0-dm-70f

2 . LIST OF THE CENTRAL INVERTERS OF KACO Model Rated Power Rated AC Voltage Protection Class Type XP00-HV 00kW *80V(±0%) IP, Indoor Transformer XP00-HV 00kW *80V(±0%) IP, Indoor Transformer XP0-HV 0kW *80V(±0%) IP, Indoor Transformer XP00-HV-TL 00 kw *90V(±0%) IP, Indoor Transformerless XP0-HV-TL 0 kw *90V(±0%) IP, Indoor Transformerless XP0-HV-TL 0 kw *90V(±0%) IP, Indoor Transformerless XP00-HV-TL 00 kw *70V(±0%) IP, Indoor Transformerless XP0-HV-TL 0 kw *70V(±0%) IP, Indoor Transformerless BP000 TL ID 000kW *70V(±0%) IP, Indoor Transformerless BP00 TL ID 000kW *70V(±0%) IP, Indoor Transformerless BP00 TL OD 00kW *70V(±0%) IP, Outdoor Transformerless BP TL OD kw *70V(±0%) IP, Outdoor Transformerless XP00-OD-TL 00kW *70V(±0%) IP, Outdoor Transformerless XP0-OD-TL 0kW *70V(±0%) IP, Outdoor Transformerless BP70 TL OD 70kW *70V(±0%) IP, Outdoor Transformerless BP87 TL OD 87kW *70V(±0%) IP, Outdoor Transformerless BP000 TL OD 000kW *70V(±0%) IP, Outdoor Transformerless Table. List of central Inverters in compliance with IEC /

3 Model Rated Power Rated AC Voltage Protection Class Type XP0U-TL 0kW *70V(±0%) NEMAR, Outdoor Transformerless BP000 TL OD 000kW *70V(±0%) NEMAR, Outdoor Transformerless BP00 TL OD 000kW *70V(±0%) NEMAR, Outdoor Transformerless Table. List of central Inverters in compliance with UL Table & Table show the list of central inverter models of KACO, which can be connected to medium voltage transformer. KACO s solar inverters are classified into types : transformer type and transformerless type. Unlike transformer inverters, the transformerless inverters don t have transformers inside, so their medium voltage transformers must be designed according to the guide when they need to be connected with external medium voltage transformers. /

4 . TECHNICAL PROPERTIES Medium voltage transformer that is connected with transformerless solar inverter must comply with following technical specifications:. The transformer must be suitable for PWM (Pulse Width Modulation) Inverter. The transformer should be designed such that its magnetic flux is not saturated even if % of DC current flow on its low voltage winding. Also the transformer should be designed and tested in accordance with ANSI/IEEE, NEMA, IEC and Department of Energy standards.. The transformer must be designed considering the voltages that arise during pulsed operation of the inverter. The voltages can reach a magnitude of maximum ±00 V reference to ground. The rms value of the voltages reference to ground is maximum 700V. (See Fig.) MV Transformer V 0 Conductor voltage regarding ground Fig. KACO central inverter with Double-winding Transformer Fig. Conductor voltage to ground and line-to-line voltage /

5 . The transformer must be designed for voltages on its low voltage windings that can exhibit a voltage gradient dv/dt of up to 00V/µs reference to the ground. The line to line voltages must be sinusoidal.. A shield winding that is grounded to the tank is necessary between the low voltage windings and the high voltage windings. This shield plate must be designed to protect against the heat due to eddy current by the flux of both the low voltage winding and the high voltage winding. This serves as an additional dv/dt filter.. In ambient temperatures off up to 0 C the transformer must have a current load capability of 0 %. Further information can be found in the following documents: KACO central inverter data sheet Power derating of KACO central inverter. During thermal rating, the load curve and the ambient conditions at the respective installation site should be taken into account. 7. KACO new energy recommends to use a transformer with a tap changer on the high voltage side that enables an alignment to the voltage level of the medium voltage grid. Our recommendation is taps with.% resolution. 8. The country-specific grid frequency should be taken into consideration. 9. The country specific standards valid should be taken into consideration. /

6 . REQUIREMENTS FOR MEDIUM-VOLTAGE TRANSFORMERS, THAT ARE CONNECTED TO CENTRAL INVERTER The transformer shown in Fig. is a double-winding transformer. Its low-voltage side is connected to KACO central inverter of which rated output voltage is 70V, and its high voltage side is for connection to the medium-voltage grid in Europe which is 0kV typically. However, other high voltages are also available: 0 kv, kv, kv, kv, 7 kv, 0 kv,.kv or kv etc. MV Transformer Fig. KACO central inverter with Double-winding Transformer This transformer must comply with the following technical specifications:. Equivalent series impedance between low voltage and high voltage winding: The equivalent series impedance Z(%) of the transformer must be %. Impedance voltage tolerance limits of. % ~. % must be maintained. This value can be determined when the highvoltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. (see Fig.). Fig. Equivalent circuit with short circuited high voltage winding /

7 . Equivalent series impedance Z(%) of the double-winding transformer: To summarize of the contents in Article, the equivalent series impedance Z(%) of the doublewinding transformer can be shown as followed. Z L is the equivalent series impedance of low voltage winding, and Z H is the equivalent series impedance of high voltage winding. Z H (%) Z La (%) Fig. Equivalent series impedance Z(%) of double-winding transformer. No neutral point is required on the low voltage side. Nevertheless, if a neutral point shows up on the low voltage side, this neutral point must not be either connected or grounded.. Double-winding transformers with varying windings each on the high voltage side and the low voltage side can be used. For example YNd, YNd, YNd or Dy, Dy, Dy with an ungrounded neutral point on the low voltage side (see Fig.) Fig. Diagram of double-winding transformer 7/

8 . REQUIREMENTS FOR MEDIUM-VOLTAGE TRANSFORMERS, THAT ARE CONNECTED TO CENTRAL INVERTERS The transformer shown in Fig.7, is a dual stacked (four-winding) transformer. Its low-voltage side is connected to KACO central inverter of which rated output voltage is 70V, and its high voltage side is for connection to the medium-voltage grid in Europe which is 0kV typically. However, other high voltages are also available: 0 kv, kv, kv, kv, 7 kv, 0 kv,.kv or kv etc. MV Transformer Fig. 7 KACO central inverter with dual stacked (four-winding) transformer This transformer must comply with the following technical specifications:. Equivalent series impedance between low voltage and high voltage winding: The equivalent series impedance Z(%) of the transformer must, in relation to every inverter, be % in each case. Impedance voltage tolerance limits of. % ~. % must be maintained. This value can be determined when the high-voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time another low voltage windings are idle (see Fig.8). 8/

9 Fig.8 Equivalent circuit with short circuited high voltage winding. Equivalent series impedance between both low voltage winding: The equivalent series impedance Z(%) between both low voltage windings must be 0 %. The tolerance limits of this impedance voltage of 9 % ~ % must be maintained. This value can be determined when one of the low voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time the high voltage windings are idle (see Fig.9). Y V sc I sc Y Fig.9 Equivalent circuit with short circuited low voltage winding. Equivalent series impedance Z(%) of the dual stacked (four-winding) transformer: To summarize of the contents in Article and Article, the equivalent series impedance Z(%) of the dual stacked (four-winding) transformer can be shown as followed. Z L is the equivalent series impedance of low voltage winding, and Z H is the equivalent series impedance of high voltage winding. 9/

10 Z La (%) Z H (%) Z Lb (%) Fig. 0 Equivalent series impedance Z(%) of dual stacked (four-winding) transformer. No neutral point is required on the low voltage side. Nevertheless, if a neutral point shows up on the low voltage side, this neutral point must not be either connected or grounded.. dual stacked (four-winding) transformers with varying windings each on the high voltage side and the low voltage side can be used. For example YNdd, YNdd, YNdd or Dyy, Dyy, Dyy with an ungrounded neutral point on the low voltage side (see Fig.). Fig. Diagram of dual stacked (four-winding) transformer 0/

11 . REQUIREMENTS FOR MEDIUM-VOLTAGE TRANSFORMERS, THAT ARE CONNECTED TO CENTRAL INVERTERS The transformer shown in Fig. is a section-winding transformer.(refer to the appendix) Its low-voltage side is connected to KACO central inverter of which rated output voltage is 70V, and its high voltage side is for connection to the medium-voltage grid in Europe which is 0kV typically. However, other high voltages are also available: 0 kv, kv, kv, kv, 7 kv, 0 kv,.kv or kv etc. MV Transformer Fig. KACO central inverter with section-winding transformer This transformer must comply with the following technical specifications:. Equivalent series impedance between low voltage and high voltage winding: The equivalent series impedance Z(%) of the transformer must, in relation to every inverter, be % in each case. Impedance voltage tolerance limits of. % ~. % must be maintained. This value can be determined when the high-voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time another low voltage windings are idle (see Fig.). /

12 Fig. Equivalent circuit with short circuited high voltage winding. Equivalent series impedance between both low voltage winding: The equivalent series impedance Z(%) between both low voltage windings must be 0 %. The tolerance limits of this impedance voltage of 9 % ~ % must be maintained. This value can be determined when one of the low voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time the high voltage windings are idle (see Fig.). I sc V sc Y Y Y Fig. Equivalent circuit with short circuited low voltage winding. Equivalent series impedance Z(%) of the section -winding transformer: To summarize of the contents in Article and Article, the equivalent series impedance Z(%) of the section -winding transformer can be shown as followed. Z L is the equivalent series impedance of low voltage winding, and Z H is the equivalent series impedance of high voltage winding. /

13 Z La (%) Z H (%) Z Lb (%) Z Lc (%) Fig. Equivalent series impedance Z(%) of section-winding transformer. No neutral point is required on the low voltage side. Nevertheless, if a neutral point shows up on the low voltage side, this neutral point must not be either connected or grounded.. Section-winding transformers with varying windings each on the high voltage side and the low voltage side can be used. For example YNddd, YNddd, YNddd or Dyyy, Dyyy, Dyyy with an ungrounded neutral point on the low voltage side (see Fig.). Fig. Diagram of section-winding transformer /

14 . REQUIREMENTS FOR MEDIUM-VOLTAGE TRANSFORMERS, THAT ARE CONNECTED TO CENTRAL INVERTERS The transformer shown in Fig. is a section-winding transformer.(refer to the appendix) Its low-voltage side is connected to KACO central inverter of which rated output voltage is 70V, and its high voltage side is for connection to the medium-voltage grid in Europe which is 0kV typically. However, other high voltages are also available: 0 kv, kv, kv, kv, 7 kv, 0 kv,.kv or kv etc. MV Transformer Fig. 7 KACO central inverter with section-winding transformer This transformer must comply with the following technical specifications:. Equivalent series impedance between low voltage and high voltage winding: The equivalent series impedance Z(%) of the transformer must, in relation to every inverter, be % in each case. Impedance voltage tolerance limits of. % ~. % must be maintained. This value can be determined when the high-voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time another low voltage windings are idle (see Fig.8). /

15 Fig.8 Equivalent circuit with short circuited high voltage winding. Equivalent series impedance between both low voltage winding: The equivalent series impedance Z(%) between both low voltage windings must be 0 %. The tolerance limits of this impedance voltage of 9 % ~ % must be maintained. This value can be determined when one of the low voltage winding is short-circuited and the voltage on the other low voltage winding is increased until the nominal current flows. At the same time the high voltage windings are idle (see Fig.9). I sc V sc Y Y Y Y Fig.9 Equivalent circuit with short circuited low voltage winding. Equivalent series impedance Z(%) of the section -winding transformer: To summarize of the contents in Article and Article, the equivalent series impedance Z(%) of the section -winding transformer can be shown as followed. Z L is the equivalent series impedance of low voltage winding, and Z H is the equivalent series impedance of high voltage winding. /

16 Z La (%) Z H (%) Z Lb (%) Z Lc (%) Z Ld (%) Fig. 0 Equivalent series impedance Z(%) of section-winding transformer. No neutral point is required on the low voltage side. Nevertheless, if a neutral point shows up on the low voltage side, this neutral point must not be either connected or grounded.. Section-winding transformers with varying windings each on the high voltage side and the low voltage side can be used. For example YNdddd, YNdddd, YNdddd or Dyyyy, Dyyyy, Dyyyy with an ungrounded neutral point on the low voltage side (see Fig.). V U W W V U W V U W V U W V U W V U U U U U W W W W V V V V Fig. Diagram of section-winding transformer /

17 HVW HVW HVW LVW LVW LVW Core HVW HVW LVW LVW Core Low Voltage winding High Voltage winding Low Voltage winding Core High Voltage winding Low Voltage winding Low Voltage winding Core APPENDIX Winding technology Medium voltage transformer that is connected with transformerless solar inverter must be designed with section winding transformer. Section winding transformer Case. Dual stacked Case. Triple stacked LVW: Low Voltage winding HVW: High Voltage winding Multi-layer winding transformer Case. LLH Case. LHL 7/

18 High Voltage winding Low Voltage winding Low Voltage winding Low Voltage winding Core Case. LLLH 8/

19 B-70~7, ND Woolim Lions Valley, -8, Sangdaewon-dong, Jungwon-gu, Seongnam-si, Gyeonggido, South Korea TEL FAX NPD-0-dm-70f