XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX TRANSMISSION AND FACILITIES STUDY. Short Circuit Analysis

Transcription

1 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX TRANSMISSION AND FACILITIES STUDY Short Circuit Analysis System Operations Department System Planning Section March 2001

2 I. Introduction XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX (XXXXX) has proposed the addition of a 250 MW generator near Newman 345 kv Substation or near Rio Grande 115 kv Substation in the year In the first proposed interconnection scenario, the new generator would interconnection to EPE's Newman 345 kv bus. In the second scenario, the interconnection would be on EPE's Diablo-Rio Grande 115 kv lines. In either case, the available fault currents on the EPE system will increase and consequently a fault analysis study was performed to determine if EPE s existing substation circuit breakers (in the substations electrically near the new generation) have adequate short circuit interruption duties. II. One alternative is to place a 250 MW generator at a new switching station (Newbus 115 kv) near Rio Grande 115 kv Substation and connect from the new generator site to this new switching station by two short 115 kv transmission lines. Also, the two existing Rio Grande-Diablo 115 kv lines will be tapped into the new switching station. Another alternative is to place a 250 MW generator near Newman 345 kv Substation and connect from the new generator site to the Newman 345 kv bus by two short 345 kv transmission lines. Although the transmission line distances are unknown at this time, a nominal conductor length of approximately 2500 feet was used, consisting of 954 kcmil 45/7 ACSR Rail, 2-conductor bundles per phase. The positive sequence impedance of each of these lines is: Z 1 = J per unit (100 MVA base) EPE determined an estimated zero sequence impedance, based on standard construction and spacing, for these lines of: Z 0 = J per unit (100 MVA base) The proposed generator will be connected to the 115 kv or 345 kv transmission system through a 330 MVA, 21/115 kv (or 21/345 kv) step-up transformer, with rated short circuit impedances of 15% each at a 330 MVA base. The following XXXXXXXXXXXXXXXX - Page 2 - El Paso Electric Company

3 impedances were modeled in the short circuit analysis for the step-up transformer: Z = J per unit (100 MVA base) The new generator is defined as 270 MVA with the following reactance values on the generator MVA base: X d = Direct Axis Synchronous Reactance = 1.95 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 Newman 345 kv Substation and the substations immediately connected to it for the new Newman 345 kv generation scenario. Following that, maximum fault currents were determined at the Newbus 115 kv Substation and the substations immediately connected to it for the Rio Grande 115 kv area new generation scenario. In addition, maximum fault currents were determined for the Newman 115 kv, Rio Grande 115 kv, and Rio Grande 69 kv buses for both scenarios. The resulting maximum fault currents were 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 size of the circuit breakers used by EPE at the 345 kv, 115 kv, and 69 kv levels 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 Newman B 40, B 40, B 40, B 40,000 Newman , ,000 Breaker Breaker Interruption XXXXXXXXXXXXXXXX - Page 3 - El Paso Electric Company

4 Newman , N , , , N , , N , N , , , N , , , N , , N , N , , N , N , , N ,000 Arroyo B 40, B 40, B 40, B 40, B 40, B 40, B 40,000 Caliente B 40, B 40, B 50, B 40, B 40,000 Luna ,000 Breaker Breaker Interruption Luna , ,000 XXXXXXXXXXXXXXXX - Page 4 - El Paso Electric Company

5 , , , , ,000 Rio Grande B 40,000* B 23, B 23, B 40, B 40, B 23, B 23, B 40, B 40,000* B 23, B 23, B 40,000 Rio Grande ,000* ,000* , , , , , , B 31, , , B 31, , ,000 Diablo K 40, B 40,000 XXXXXXXXXXXXXXXX - Page 5 - El Paso Electric Company

6 Breaker Breaker Interruption B 40, B 40, B 31, B 40, B 40,000 *Currently, these breakers are rated in the neighborhood of 20,000 amperes but are expected to be replaced with 40,000 ampere rating breakers as part of the normal breaker replacement program. The short circuit analysis was first performed with no new XXXXX generation. This gave the benchmark fault duties of the circuit breakers. Following this, the new generator was added to the modeling and the short circuit study was executed again. The incremental between these two studies gave the impact of the new generator on the existing circuit breakers in the EPE system. The short circuit (fault) currents for each case at all of the possibly impacted substations are: Three Phase Line to Ground: With New Generation No New Generator Newman Substation Faulted Fault Current (Amps) Fault Current (Amps) Newman 345 kv Bus 6, ,187.3 Newman 115 kv Bus 22, ,367.0 Luna 345 kv Bus 7, ,610.8 Arroyo 345 kv Bus 5, ,943.4 Caliente 345 kv Bus 5, ,079.4 Rio Grande 115 kv Bus 18, ,529.6 Rio Grande 69 kv Bus 18, ,687.4 XXXXXXXXXXXXXXXX - Page 6 - El Paso Electric Company

7 Single Phase Line to Ground: With New Generation No New Generator Newman Substation Faulted Fault Current (Amps) Fault Current (Amps) Newman 345 kv Bus 6, ,981.7 Newman 115 kv Bus 26, ,119.4 Luna 345 kv Bus 6, ,335.4 Arroyo 345 kv Bus 4, ,256.0 Caliente 345 kv Bus 5, ,083.4 Rio Grande 115 kv Bus 20, ,404.6 Rio Grande 69 kv Bus 21, ,976.8 Three Phase Line to Ground: With New Generation No New Generator Rio Grande Substation Faulted Fault Current (Amps) Fault Current (Amps) Rio Grande115 kv Bus 18, ,135.4 Diablo 115 kv Bus 17, ,327.3 Rio Grande 69 kv Bus 18, ,039.0 Newman 115 kv Bus 22, ,734.1 Single Phase Line to Ground: With New Generation No New Generator Rio Grande Substation Faulted Fault Current (Amps) Fault Current (Amps) Rio Grande115 kv Bus 20, ,633.0 Diablo 115 kv Bus 17, ,051.9 Rio Grande 69 kv Bus 21, ,501.6 Newman 115 kv Bus 26, ,057.6 Comparing these fault currents to the appropriate existing circuit breaker interruption ratings shows that the interconnection of the new generator on EPE s system will cause certain circuit breakers to operate outside their design ratings (see below). XXXXXXXXXXXXXXXX - Page 7 - El Paso Electric Company

8 V. Results and Conclusions A short circuit study was performed on the EPE system comparing the maximum fault current on the system at various substations. The results of this study show that with the Rio Grande 115 kv Substation area new generation scenario, six 115 kv breakers at Rio Grande Substation will need to be replaced. The maximum fault current at the Rio Grande 115 kv bus, under this scenario, will be 25,633 amperes. Consequently, the following existing breakers will need to be replaced: Breaker Breaker Interruption Rio Grande B 23, B 23, B 23, B 23, B 23, B 23,000 For the scenario where new generation is to be located near the Newman 345 kv Substation, all circuit breakers have adequate fault current capability and no replacements will be necessary. XXXXXXXXXXXXXXXX - Page 8 - El Paso Electric Company

9 V. Certification This was performed pursuant to the Agreement for a Transmission and Facilities Study dated July 7, 2000, between El Paso Electric Company Transmission & Distribution Division (EPE T&D) and XXXXXXXXXXXXXXXXXXXXXXXXX (XXXXX). This Study analyzes the EPE circuit breaker interruption ratings with the addition of new generation as per the Transmission and Facilities: Study Scope (Study Scope) dated July 20, This Study Scope was later verbally amended by XXXXX, primarily with regards to study scenarios and generator sizes. As per XXXXX, the data representation for the new XXXXX area generator was based on data previously used in other studies conducted by EPE T&D. Please note that if the actual generation parameters and technical constants of the generator(s) actually constructed by XXXXX are different than from what was utilized in this Study, the Short Circuit analysis must be re-done at XXXXX expense. This study analyzed the addition of one 270 MVA (250 MW) gas turbine/generator with output at 21 kv and depending on location, either a 21/115 kv or 345 kv, 330 MVA step-up transformer. EPE performed these short circuit studies. Name: Title: Signature: Dennis H. Malone Supervisor, System Planning Dennis H. Malone Date: March 27, 2001 XXXXXXXXXXXXXXXX - Page 9 - El Paso Electric Company