Short Circuit Analysis with New Generation Proposed by XXXXXXXXXXXXXXXXXXXXXX Pursuant to a Transmission and Facilities Study

Transcription

1 Short Circuit Analysis with New Generation Proposed by XXXXXXXXXXXXXXXXXXXXXX Pursuant to a Transmission and Facilities Study Study Performed by El Paso Electric Company System Planning Section - 1

2 I. Introduction Short Circuit Analysis with New Generation Connected to Luna 345 kv Bus On March 17, 2000, El Paso Electric Company (EPE) and XXXXXXXXXXXXXXXXXXXXX (XXXX) signed an Agreement for a Transmission and Facilities Study with regard to the construction and interconnection of MW of new generation (two gas turbines and a steam turbine in a combined cycle arrangement) at the Luna 345 kv bus. The powerflow and stability analysis of this study is being performed by EPE and will be issued under a separate cover. When generation is added to a system, the available fault current of that system increases. Therefore, a study has been performed to determine if the Southern New Mexico existing substation circuit breakers in the substations electrically near the new generation have adequate short circuit interruption duties. II. Short Circuit Study The new generation proposed by XXXX is sited near the Luna 345 kv substation and will be interconnected to the Luna 345 kv Substation bus through a 345 kv circuit of approximately 3200 feet in length consisting of 954 kcmil 45/7 ACSR Rail, 2-conductor bundles per phase. The positive sequence impedance of this line is: Z 1 = J per unit (100 MVA base) EPE determined an estimated zero sequence impedance, based on standard construction and spacing, of: Z 0 = J per unit (100 MVA base) The generators will be connected to the 345 kv transmission through two (2) 193 MVA and a 308 MVA, 18/345 kv step-up transformers, for the gas turbines and the steam turbine, respectively. The step-up transformers have impedances of 10 % on a 116 and 185 MVA for each of the gas turbine and the steam turbine step-up transformer, respectively. These impedances were modeled in the short circuit analysis as: Z(gas turbines) = J per unit (100 MVA base) Z (steam turbine) = J per unit (100 MVA base) - 2

3 The new generators have the following reactance values on the generator MVA base: Gas Turbines: X d = Direct Axis Synchronous Reactance = 1.90 per unit X d = Direct Axis Transient Reactance = per unit X d = Direct Axis Subtransient Reactance = per unit Steam Turbine: X d = Direct Axis Synchronous Reactance = 2.13 per unit X d = Direct Axis Transient Reactance = per unit X d = Direct Axis Subtransient Reactance = per unit These reactance values were converted to a 100 MVA base and used to model the new generators in the short circuit study. Maximum fault currents were then determined at the Luna 345 kv and the Luna 115 kv buses, and the substations immediately connected to Luna: Arroyo 345 kv Diablo 115 kv Mimbres 115 kv Newman 115 kv Diablo 345 kv Hidalgo 345 kv Newman 345 kv The resulting fault current was then compared to the circuit breaker interruption ratings of the breakers at each of the above mentioned substations. III. Results of the Short Circuit Analysis The circuit breakers used in the Southern New Mexico System at 345 kv and 115 kv buses vary between the substations. The following is a list of the existing circuit breakers, along with the interruption rating, at each of the pertinent substations: Breaker Breaker Interruption Substation Voltage Number Rating (Amps) Arroyo B 40, B 40, B 40,000-3

4 B 40, B 40, B 40, B 40,000 Diablo B 40, B 40, B 40,000 Hidalgo , , , ,000 Luna , , , , , , , , ,000 Newman B 40, B 40, B 40, B 40,000 Diablo B 40, B 40, B 40, B 40, B 40, B 31,500 Breaker Breaker Interruption Substation Voltage Number Rating (Amps) Luna , , ,000-4

5 Mimbres , , , , ,500 Newman , , , N , , , N , , N , , , N , , , N , , N , N , , N , N , , N , N ,000 The short circuit analysis was first performed with no new generation. This gave the base case fault duties of the circuit breakers. Then the three new generators and the modifications determined from the results of the powerflow part of the study were modeled and the short circuit study was re-run. The incremental between these two studies gave the impact of the new generators on the existing circuit breakers in the Southern New Mexico system. The short circuit (fault) currents for each case at all of the possibly impacted substations are: - 5

6 Three Phase Line to Ground: No XXXX Generators With 3 XXXX Generators Substation Faulted Fault Current (Amps) Fault Current (Amps) Arroyo 345 kv Bus 5, ,767.5 Diablo 345 kv Bus 4, ,512.0 Hidalgo 345 kv Bus 6, ,387.3 Luna 345 kv Bus 7, ,935.3 Newman 345 kv Bus 6, ,796.1 Diablo 115 kv Bus 17, ,657.9 Luna115 kv Bus 8, ,523.5 Mimbres 115 kv Bus 7, ,279.6 Newman 115 kv Bus 22, ,649.2 Single Phase Line to Ground: No XXXX Generators With 3 XXXX Generators Substation Faulted Fault Current (Amps) Fault Current (Amps) Arroyo 345 kv Bus 4, ,119.9 Diablo 345 kv Bus 4, ,362.5 Hidalgo 345kV Bus 5, ,851.3 Luna 345 kv Bus 6, ,124.9 Newman 345 kv Bus 6, ,385.8 Diablo 115 kv Bus 17, ,693.9 Luna 115 kv Bus 9, ,129.0 Mimbres 115 kv Bus 7, ,563.6 Newman 115 kv Bus 26, ,670.3 Comparing these fault currents to the appropriate existing circuit breaker interruption ratings shows that the interconnection of the new generators at the Luna 345 kv Substation, in the configuration and parameters as given by XXXX, will not cause any existing circuit breaker to operate outside its design rating. IV. Results and Conclusions A short circuit study was performed on the Southern New Mexico system comparing the maximum fault current on the system at various substations: Luna Substation (both 345 kv and 115 kv) and each substation directly connected to Luna, both with and without the three new generators proposed by XXXX. The - 6

7 results of this study show that the maximum fault current with the three new generators is less than the minimum interruption rating of any effected existing circuit breaker: Maximum Minimum Circuit Breaker Fault Current with 3 Substation Interruption Rating (Amps) New Generators (Amps) Arroyo 345 kv 40,000 5,767.9 Diablo 345 kv 40,000 5,512.0 Hidalgo 345 kv 40,000 7,387.3 Luna 345 kv 40,000 11,124.9 Newman 345 kv 40,000 8,385.8 Diablo 115 kv 31,500 19,693.9 Luna 115 kv 40,000 11,129.0 Mimbres 115 kv 17,500 8,563.6 Newman 115 kv 40,000 29,670.3 Therefore, the operation of the three new generators with the parameters as given by XXXX connected to the Luna 345 kv bus will not cause any existing circuit breaker to operate outside its interruption rating limit. - 7

8 V. Certification This Short Circuit Analysis was performed pursuant to the Agreement for a Transmission and Facilities Study, dated March 17, 2000 requested by XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX. The generator, step-up transformer and new transmission line parameters were supplied by XXXXXXXXXXXXXXXXXXXXXXXXXX. The Short Circuit Analysis was performed by El Paso Electric Company. Name: Title: Dennis H. Malone Supervisor, System Planning Signature: Dennis H. Malone Company: El Paso Electric Company Date: January 10, 2001 AGREEMENT OF RESULTS: Name: Jeff Mechenbier Name: Kenneth Houston Title: Manager, Transmission Analysis Title: Director, Engineering Signature: Jeff Mechenbier Signature: Kenneth Houston Company: Public Service Company of NM Company: Texas-New Mexico Power Company Date: January 15, 2001 Date: January 10,