Independent Power Engineers

Never Trust the Machine, trust the engineer!

Who are we? IPE (Independent Power Engineers) is a nonprofit organization passionate about the power engineering industry. Our main mandate is to test and expose the different issues and dysfunctions of different power system simulation softwares. Please note that all of our tests are made available also on YouTube for transparency. Look for Independent Power Engineers on YouTube to get access to our latest videos.

Product Manufacturer Version Revision Operating system System properties

ETAP™, DIgSILENT 14, 14.1, 15 and NEPLAN 5.4 , 5.5 OTI™ (Operation Technology Inc), DIgSILENT, NEPLAN/ABB ETAP: 7.1, 7.5, 11, 11.1, 12.0,12.5 and 12.6, DIgSILENT 13, 14.1, 15 and NEPLAN 5.4 , 5.5 All Versions/Revisions Windows 7 / 64 Bit CPU @1.80GHz RAM: 2.00GB

ETAP CASE-0067 Analysis Analysis detail Events Issue

Reason Proposed solution

Transient stability algorithm Initial Load Flow, Precision= 0.0001 ,Max No. of Iteration =9999, Total Simulation Time: 1 Sec , Simulation time step= 0.001 Short circuit at Generator bus at t=0.1 sec and clearing the short circuit at t=0.2 sec 1-Difference between results of buses voltage during fault and after fault when using transient stability module of ETAP, DIgSILENT and NEPLAN 2-In ETAP when we increase amount of static load from 1,000 KVA to 12,000 KVA, the voltage in transient stability will be increased??? Estimation in transient stability engine and dynamic modeling of Motors/Generators Recommend to use a software that has more accurate modeling and calculation engine in transient stability

ETAP CASE-0067 Overview: In this document we decided to remodel a part of a real network (a part of an electrical network of a Power plant) to test transient stability engine of ETAP from version 7 to version 12.6. The model consists of one generator, three cables, two transformers, one static load and two identical induction motor.

Faulted Bus

Figure 1: Simple Network modeling

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Independent Power Engineers

Never Trust the Machine, trust the engineer!

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Motor : (4 KV, 3500 KW, PF= 92.1 %, Eff= 94.39 %, I(Locked Rotor)= 950 %, PF(Locked Rotor)= 24.97%, LRT=87%, MaxT=198.6%, Ns=1800, Nr=1800, Slip=0.66%, In=581.1 A, Model Single 2: Single cage with deep bar, Total H=1.849 , Load Model: TL=20 -84 w + 213 w^2 – 48 w^3 Number of motors: Two (2)

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Cable Type : 15 KV, R= 0.2 ohm/km , X= 0.4 ohm/km, Y=0.0), CABLE 1 Length=4.5km , CABLE 2 Length=1 km, CABLE 3 Length=0.1 km

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Transformer: V1/V2: 12.47/4.26KV, Z=6%, X/R=20, S=10 MVA

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BUS-L: 4.16 KV , BUS-M: 4.16 KV ,BUS-T1: 12.47 KV ,BUS-T2:12.47 KV, BUS-S: 12.47 KV, BUS-G: 12.47 KV

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Generator G1 and G2: (12.47 KV, 10 MW, PF= 85 %, Eff= 95 %, , Poles=4, n=1800rpm, X”d= 19%, X2= 18 %, X0= 7% , Xd= 155%, Xdu= 165% , X’d= 28%, Xl=15%, Xq= 155%, Xqu= 155%, X’q=65%, X”q=19%, T’d0= 6.5 sec, T”d0= 0.035 sec T’q0= 1.25 sec, T”q0= 0.035 sec, Round rotor, Total H=1.3 , SWING TYPE , , Qmax=6 MVAR, Qmin=-3 Mvar

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Static load: 1000 KVA, power factor= 0.8

Same modeling with same data has been done in DIgSILENT and NEPLAN Study case 1: 3 phase Short circuit will happen at “BUS-G2” at t=0.1 sec and short circuit will be cleared at t=0.2 sec The issue is to see if voltage of system motor can be recovered or not?( It should recover easily)

Figure 2: Voltages of Buses during fault and after fault, Results by using ETAP transient stability engine, static load amount is 1000 KVA

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Independent Power Engineers

Never Trust the Machine, trust the engineer!

Figure 3: Voltages of Buses during fault and after fault, Results by using DIgSILENT transient stability engine, static load amount is 1000 KVA

Figure 4: Voltages of Buses during fault and after fault, Results by using NEPLAN transient stability engine, static load amount is 1000 KVA

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Independent Power Engineers

Never Trust the Machine, trust the engineer!

Observation 1 As we can see by comparing three graphs of NEPLAN, DIgSILENT and ETAP , we can see that: Figure (2): in ETAP, the voltage of Motor bus (BUS-M), will collapse to 52 % after removing the fault Figure (3): in DIgSILENT, the voltage of Motor bus (BUS-M) will be recovered to 99 % Figure (4): in NEPLAN, the voltage of Motor bus (BUS-M) will be recovered only to 102 % Study case 2: The issue is to see if by increasing amount of static load, what will happen to amount of the buses voltage after removing fault, so we increase static load amount to 5000 KVA and 9,900 KVA and 12,000 KVA and then will run the previous scenario: 3 phase Short circuit at bus no. “BUS-G2” at t=0.1 sec and short circuit will be cleared at t=0.2 sec

Figure 5: Voltages of Buses during fault and after fault, Results by using ETAP transient stability engine, static load amount is 5000 KVA

Figure 6: Voltages of Buses during fault and after fault, Results by using ETAP transient stability engine, static load amount is 9900 KVA

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Independent Power Engineers

Never Trust the Machine, trust the engineer!

Figure 7: Voltages of Buses during fault and after fault, Results by using ETAP transient stability engine, static load amount is 12,000 KVA

If we compare figure no. 2 and figure no. 5, 6 and 7, we can see that by increasing the amount of static load, the amount of voltage will be more and this is very strange!!!!!!??????? But if we check results of DIgSILENT and Neplan, we can see that by increasing amount of static load, the voltage will be less, that is correct. If we refer to the dynamic models of motors and generators in ETAP software and compare with DIgSILENT/NEPLAN, we can see that dynamic modeling in DIgSILENT/NEPLAN are more accurate with more details than ETAP, also in ETAP, some parameters has been ignored and also some estimation methods has been used in modeling and calculation engine, this is the reason of difference between results of ETAP and DIgSILENT/NEPLAN. Following shows the difference between results of ETAP , DIgSILENT and NEPLAN in case No.1 Software ETAP DIgSILENT NEPLAN

Voltage of Motor Bus(BUS-M) % when amount of static load is 1000 KVA T=0.1(+) sec T=0.2 sec T=0.3(+) sec T=0.5 sec T=0.75 sec T=1.0 sec 100% 62% 64% 61% 59% 53% 100% 70% 75% 89% 95% 99% 106% 85% 90% 94% 95% 102%

ETAP CASE-0067 Explanation: It seems that there is some estimation in calculation engine of Transient stability in ETAP software so the results in transient stability will be calculated with high estimation and this is why the results are far from real network results. We recommend for doing transient stability analysis in real networks use software‘s with high accurate modeling and deny to use software with estimation algorithms/Engine

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