Principal Research Results

Development of ATC Evaluation Method with Dynamic Stability
Constraints−Development of Efficient Contingency Screening Method−
Background
Fast and accurate evaluation of ATC (additional power which can be transferred over transmission network between asource and a sink) is essential to efficient use of networks in the deregulated environment. An ATC assessment involves a large number of contingency analyses based on supply/demand scenarios with various transaction volumes. Therefore, evaluation of ATC withdynamic stability constraints, which is important to Japanese interconnected network, requires much computation time, and development of efficient evaluation method is needed.
A promising method of efficient ATC assessment is an application of contingency screening method, where only contingencies chosen by screening method are closely examined by time domain simulation. However, conventional contingency screening
methods focus mainly on first-swing instability and fail to identify severe contingencies with multi-swing instability.

Objectives
Development of efficient contingency screening method, which can accurately identify severe faults with both first-swinginstability and multi-swing instability and contribute to the efficiency of ATC evaluation

Principal Results
1. A novel contingency screening method is developed, which utilizes both energy function method and eigenvalue analysis. The mainfeatures of the proposed method are as follows (Figure 1):1) It can accurately find out severe contingencies with both first-swing instability and multi-swing instability2) Supply/demand scenarios where time domain simulation is required are identified based on information obtained by energyfunction method.
2. A number of numerical examples show that the proposed method has very good performance from the viewpoint of accuracy ofscreening (Table 1). Examples also show that the computation time of ATC assessment is reduced to 1/2 ~ 1/4 by application of theproposed method (Table 2).

Future Developments
Further development is needed to make the proposed method more applicable to multi-swing instability cases, where nonlinearity has much effect on the stability.
Main Researcher: Masaki Nagata, Ph.D.,
Research Engineer, Electric Power Systems Sector, System Engineering Research Laboratory
Reference“An efficient contingency screening scheme for ATC assessment with transient stability constraints”, CRIEPI Report, T03016, March
2004 (in Japanese)704. Power Delivery - Cost reduction and ensuring reliability of power delivering

Transaction Volume P=0Index
dexScreening
PartCases to be screened

Contingency Screening

Transaction Volume P=P0 (>0)
Detailed
DynamicStability
Assessment
Part

P = P + ΔP

Mainly, cases with
first-swing instability

CContingencies
screened

Dynamic security Assessment(DSA)(Detailed analyses ofcontingencies screened by timedomain simulation)
NSEF

Instability ?
YEND● Screening IndicesMethod of screening
・Based on energy function method
・Apply longer fault clearing time (e.g. 0.2[sec]) thanusual to emphasis the severity of contingency
・Identify contingencies as “severe”, where system
is unstable just after fault is cleared・Supply/demand scenarios, where detailed analysis
is required, are identified based on the change innumber of “severe” faults as transaction volume
increases

・Based on eigenvalue analysis
・Utilize the sensitivities of the following quantities
with respect to transaction volume
Mainly, cases with1) Damping of swing modesSEV
multi-swing instability 2) Particiption factors of the generator, which is“source” of transaction, with respect to swing modes
・ Identify a given number of contingencies as“severe”, which have largest sensitivities

ATC = P in the previous stepFig.1 The proposed ATC assessment procedure and contingency screening method
Table 1 Accuracy of the proposed contingency screening method

ModelPower
SystemBase case
Scenario

Number of transaction cases (*1)(number of caseswith multi-swing instability)

PeakNight
Peak
Night

EAST30
WEST30

84
84
92
98358

Total

Number of cases, where the proposed method
identifies the severest faults×00022○84849296356(60)
(36)
(82)
(94)

*1...Number of cases among 100 cases (all combinations of 10 sources and 10 sinks), where dynamic stability constraints has limiting effect on transmission
capability

Table 2 ATC evaluation results of 10 transaction cases in Table 1
Conventional method (*2)
Model power
Transaction
system & Basepatterncase scenario

EAST30,Peak

WEST30,PeakATC[MW](*1)

Type ofinstability

Number ofcontingencies inDSA

Computation
Time[Sec]

Proposed method
Number ofcontingencies
screened

Computation
Time[Sec]

Ratio toconventional
methodIndex identifing
the severest
fault (*3)

E1340 First-swing

136

390.2

15222.40.57

SEF，SEV

E26680 Multi-swing

136

2284.513502.6

0.22

SEVE32030 Multi-swing

136

880.4

12211.3

0.24

SEF

E4

2600 First-swing

136

944.7

11274.00.29

SEF，SEVE55250 Multi-swing

136

1584.014396.0

0.25

SEF，SEV

W1

170 Multi-swing

80

327.6

12144.1

0.44

SEF

W2980 First-swing

80

264.6

10132.3

0.50

SEF，SEV

W3

3500 Multi-swing

80

731.4

16175.50.24

SEF，SEV

W42910 Multi-swing

80528.612163.90.31

SEVW53950 Multi-swing

80688.8

12179.1

0.26

SEF*1…In all cases, ATC obtained by the proposed method is identical to ATC by conventional method.
*2…Conventional method doesn't utilize contingency screening and all contingencies are considered in DSA.
*3...SEF is based on energy function method, SEV is based on eigenvalue analysis.

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