EL PASO ELECTRIC COMPANY SHORT CIRCUIT ANALYSIS FOR XXX S PROPOSED GENERATION INTERCONNECTION

Transcription

1 EL PASO ELECTRIC COMPANY SHORT CIRCUIT ANALYSIS FOR XXX S PROPOSED GENERATION INTERCONNECTION El Paso Electric Company System Operations Department System Planning Section August 2006

2 I. INTRODUCTION The interconnection of new generating units into a transmission system will increase the fault current contribution into the system. Therefore, as part of this Study, a short circuit analysis was performed to determine if the additional fault current contribution from the XXX wind generators into the EPE transmission system will cause any of EPE s existing substation circuit breakers to exceed their interruption ratings. II. SHORT CIRCUIT STUDY MODELING The wind generation proposed by XXX is sited approximately 53 miles east of EPE s Amrad 345 kv substation. Data provided by XXX indicates that the wind turbines will be interconnected on the Amrad-Artesia 345 kv transmission line through two 150/200/250 MVA, 34.5/345 kv step-up transformers. Each step-up transformer has a positive sequence impedance of 8.5% and a zero sequence impedance of 9% on a 150 MVA base. The step-up transformer impedances modeled in the short circuit analysis for both step-up transformers were: Z 1 (step-up) = J per unit (150 MVA base) Z 0 (step-up) = J per unit (150 MVA base) Equivalent reactance data for the modeling of the wind machines in EPE s short-circuit data base was difficult to obtain from XXX and their consultants. However, Public Service company of New Mexico (PNM) has experience in modeling wind machines for a short-circuit analysis and they provided assistance in obtaining a short-circuit model for these machines. PNM contacted its GE representative, who in turn provided the shortcircuit modeling for the wind generator. GE stated that an official model for the 1.5 MW turbine has not been developed as of yet. Therefore, they recommended the use of their 1.67 MVA model at a 0.90 power factor to achieve the 1.5 MVA output of each machine. The following equivalent reactance values for the wind machines were supplied by GE and modeled in the EPE short circuit data base: X d = Direct Axis Synchronous Reactance = 0.28 per unit X d = Direct Axis Transient Reactance = 0.28 per unit X d = Direct Axis Subtransient Reactance = 0.28 per unit R = Direct Axis Resistance = 0.01 per unit These reactance values were also based on a 150 MVA base and used to model the wind generator in the short circuit study. The location of the XXX wind machines on the Amrad-Artesia 345 kv line also required the line impedances to be recalculated. Therefore, the Amrad-Artesia line was divided Short Circuit Analysis for XXX s 1 El Paso Electric Company

3 into two sections, the Amrad-XXX 345 kv line and the XXX-Artesia 345 kv line. The line impedance of the Amrad-Artesia line (125.4 miles in length) was proportioned according to the location of the XXX generators (53 miles east of Amrad Substation). Therefore, the Amrad-XXX 345 kv line impedance was modeled as 42.3% (53/125.4) of the total Amrad-Artesia 345 kv line impedance and the XXX-Artesia 345 kv line impedance was modeled as 57.7% (72.4/125.4) of the total Amrad-Artesia 345 kv line impedance. The impedances modeled for each of the XXX 345 kv line segments are shown below: AMRAD-XXX LINE IMPEDANCE XXX-ARTESIA LINE IMPEDANCE Z 1 = j Z 1 = j Z 0 = j Z 0 = j In addition to the new XXX generation, all existing and proposed third party generation ahead of the XXX project in the study queue were modeled in the data base. These generation projects included the following: 570 MW of existing generation (Luna Energy Facility) interconnected at Luna 345 kv Substation and scheduled to WECC. 141 MW of existing generation (Afton) interconnected at Afton 345 kv Substation and scheduled through EPE s Arroyo PST. 60 MW of existing generation interconnected at Tri-State Generation and Transmission Association, Inc. s (Tri-State) Hidalgo 115 kv Substation and scheduled to WECC. 80 MW of existing generation interconnected at Texas-New Mexico Power Company s (TNP) Lordsburg 115 kv Substation and scheduled to WECC. 94 MW of generation (presently being constructed) interconnected at Afton 345 kv Substation and scheduled to WECC. Two cases were developed to perform this analysis, one with and one without the XXX generation. Three phase and single-line-to-ground faults were then simulated at the Amrad and Artesia 345 kv buses in each of the two cases. The difference between the fault current values in the two cases is the additional fault current contribution from the XXX wind generation. Fault currents were monitored at the buses closest to where the XXX generation will be interconnected, since this is where the greatest fault current contribution can be attributed to the XXX project. The buses monitored included the following: Short Circuit Analysis for XXX s 2 El Paso Electric Company

4 Amrad 345 kv Amrad 115 kv Artesia 345 kv Caliente 345 kv Caliente 115 kv The resulting 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 following is a list of existing circuit breakers and their interruption ratings at each of the substations monitored in this study: Breaker Breaker Interruption Substation Voltage Number Rating (Amps) Amrad B 40, B 40, B 40, B 40,000 Amrad B 40, B 40, B 40, B 40,000 Caliente B 40, B 40, B 40, B 40, B 40,000 Caliente B 40, B 40, B 40, B 40, B 40, B 40, B 40, B 40, B 40,000 Artesia 345 4R10 40, R05 40,000 Short Circuit Analysis for XXX s 3 El Paso Electric Company

5 The short circuit analysis was first performed without the XXX generation interconnected into the EPE system, but with all other third party generation projects in. This analysis produced the base case short-circuit values of the existing system. The proposed XXX generation was then modeled into the system and a short-circuit analysis was again performed with the XXX generation installed. The incremental difference between the two cases determined the increase in short-circuit contribution to the existing EPE transmission system due to the proposed XXX generators. If this incremental difference causes any of the existing substation circuit breakers to exceed their maximum interruption ratings, they will have to be replaced. In addition to the buses shown above, faults were simulated at the XXX 345 kv and XXX 34.5 kv buses. This was done to provide XXX with an estimate of the fault current contribution from the wind machines during a contingency of the XXX wind generation. This will give XXX an indication of the size of circuit breakers it will need to protect its 34.5 kv and 345 kv buses. The short circuit (fault) currents with and without the XXX generation at the buses listed above are shown below: Three Phase Line to Ground: Without XXX Gen With XXX Gen Fault Current Fault Current Faulted Bus (Amps) (Amps) Amrad 345 kv Bus 3,507 4,683 Amrad 115 kv Bus 7,000 8,004 Caliente 345 kv Bus 6,599 7,481 Caliente 115 kv Bus 14,760 15,632 Artesia 345 kv Bus 1,507 2,035 XXX 34.5 kv Bus - 42,176 XXX 345 kv Bus - 3,628 Single Phase Line to Ground: Without XXX Gen With XXX Gen Fault Current Fault Current Faulted Bus (Amps) (Amps) Amrad 345 kv Bus 3,082 4,239 Amrad 115 kv Bus 5,976 7,062 Caliente 345 kv Bus 6,328 6,965 Caliente 115 kv Bus 15,842 16,593 Artesia 345 kv Bus 965 1,475 XXX 34.5 kv Bus - 36,988 XXX 345 kv Bus - 3,672 Short Circuit Analysis for XXX s 4 El Paso Electric Company

6 IV. Results and Conclusions This short circuit analysis was performed on the EPE system comparing the maximum fault current on the system at various substations both with and without the proposed XXX generation. The table below shows the results of the short circuit analysis with the proposed XXX generation interconnected into the EPE transmission system. Short Circuit Results With Proposed XXX Generation Maximum Maximum Circuit Breaker Fault Current With Interruption Rating XXX Generation Bus (AMPS) (AMPS) Amrad 345 kv Bus 40,000 4,683 Amrad 115 kv Bus 40,000 8,004 Caliente 345 kv Bus 40,000 7,481 Caliente 115 kv Bus 40, Artesia 345 kv Bus 40,000 2,035 XXX 345 kv Bus - 3,672 XXX 34.5 kv Bus - 42,176 Results of the analysis indicate that the maximum fault currents are well within the maximum circuit breaker ratings at each of the buses analyzed. Therefore, the interconnection of the XXX wind machines into the EPE transmission system as modeled in this analysis will not cause any existing EPE circuit breaker to operate outside its interruption rating limit. The results also indicate that XXX will need to install 50,000 Amp circuit breakers at its 34.5 kv bus to protect its system in the event of a loss of all its wind generation. Short Circuit Analysis for XXX s 5 El Paso Electric Company

7 V. Certification This Short Circuit Analysis was performed as part of the Generation Interconnection Feasibility Study requested by XXXXXXXXXXXXXXXXXXX (XXX). The step-up transformer data was supplied by XXX. The model for the wind machine was provided by Public Service Company of New Mexico s (PNM) representative from General Electric (GE). GE stated that it presently does not have an official short-circuit model for XXX s proposed 1.5 MVA wind machines. The model they provided was for a 1.67 MVA wind machine at a 0.90 power factor to achieve the 1.5 MVA rating of each of the XXX wind machines. This was the best data available to model the XXX wind turbines into the sort-circuit data base at the time the study was performed. If XXX decides to continue with its proposed interconnection, it will need to provide a more accurate representation of the wind machines in order for EPE to perform a more accurate short-circuit analysis of its transmission system with the XXX generation installed. This Short Circuit Analysis was performed by El Paso Electric Company (EPE). Name: Title: Dennis H. Malone Manager, System Planning Signature: Company: El Paso Electric Company Date: Short Circuit Analysis for XXX s 6 El Paso Electric Company