Assessment of Risk Against Regulator Requirements for Duration of Long Supply Interruptions

Mohd Ikhwan Muhammad RidzuanDr Sasa DjokicThe University of Edinburgh, UKm.muhammad-ridzuan@ed.ac.uk

Introduction

• Distribution network operators (DNOs) have to make sure the frequency and duration of interruptions experienced by their customer are within specified or agreed limits and targets

• DNOs may be rewarded, penalized or liable for compensation based on their actually achieved reliability performance

• An important aspect of the related analysis is assessment of RISK that DNOs face (based on relevant characteristics and operation strategies of their networks and other influential factors)

Input Data & Parameters: Fault Rates & Repair Time

Input Data & Parameters: Daily Variation of Interruption Probability

Continuity of Supply Requirements: UK Security and Quality of Supply

Continuity of Supply Requirements: UK Guaranteed Standard of Performance

Continuity of Supply Requirements: Italian Supply Quality Standard

Continuity of Supply Requirements: Italian Guaranteed Standard of Performance

Test Network500kVA

Transformer

11kV 0.4kV

ZT=2.04 + j9.28 (p.u. on 100MVA)

190 customersPMAX= 2.27kW/customer Total Load MAX= 431.3kW (at 1p.u.)

U1

U2

U3

U4

U5 U6

U7

U8

U9 U10

U11

U12 U13

U14 U15U16 U17

U18

U19

78.6m

36m

85m

32m 90m 41m 35m 33m 17m

73m 67m

24m 52m

93m 68m 40m

70m

53m 12m

32m

41m

15m 80m 85m

27m 26m 53m

90m

82m

40m 17m

DE

E

A A B C D E

E E

E E

E E E

E

E EE

E

D D E

C D EE

D

E E

L

L

L

L

L L

L

L

L

L

L

L L

L L

L L

L

L

(15 cust.)

(15 cust.)

(12 cust.)(14 cust.) (9 cust.)

(12 cust.)(12 cust.) (9 cust.)

(12 cust.) (6 cust.)

(9 cust.) (6 cust.)

(6 cust.)

(15 cust.) (15 cust.)

(8 cust.) (8 cust.)

(6 cust.)

(4 cust.)

* L type line length = 30m

To another Primary

Substation

375m 375m 375m 375m 375m 375m 375m 375m 150m

11kV

33kV P P P P Q Q Q Q Q

*2 *3

*4 *5 *6

Reflection Centre

Transformer

Circuit Breaker

Fuse

Disconnector (n. open)

Total : 9120 customers

(48 transformers x190 customers/transformer)

PMAX = 2.27kW/customer

Total LoadMAX = 20.7MW

Zeq=0.063206+j0.0356383 (p.u. on 100MVA)

500kVA

Radial LV Distribution (Underground Cable)

ZLV=5.377+j10.1925 (p.u. on 100MVA)

0.4kV

15MVA

15MVA

Grid Supply System

Zsys

Zsys=0.0269+j0.1822(p.u. on 100MVA)

*2

*6

*5

*4

*3543MVA Source

Typical UK urban distribution networkMV: Meshed (but operated radially in normal conditions), with an alternative supply point (unrestricted support)LV: Radial (3-phase & 1-phase service connections)

Risk Assessment Procedures

Analytical Approaches:Based on mathematical models, which typically limit outputs to oneset of results, e.g. mean values of reliability indices, corresponding tothe specified input mean data.

Offer only a general “snapshot” characterisation of the analysedsystem, as they will always provide the same set of output results forthe same set of input data, parameters and models.

Probabilistic (Monte Carlo) Approaches:Allow to model a wide range of variations of practically all inputparameters and data in one or few simulation/calculation set-ups,without the need to repeat calculation after a change in input data.

Outputs are reliability indices, which are typically presented asprobability distributions with the corresponding mean values.

Risk Assessment ProceduresWHY COMBINE PROBABILISTIC & ANALYTICAL RELIABILITY

ASSESSMENT?

Probabilistic Approaches give probability distributions of customerinterruptions (which customers will be interrupted and how frequently) and probability distributions of interruption durations

Analytical Approaches could incorporate Regulator Requirements, if actual limits are used as input data For example, if we assume that every faulted component has repair time of exactly 18 hours, with the same duration applied for transfer to alternative supply and time required for network reconfiguration, the worst possible network reliability performance for which there will still be no penalty incurred due to supply interruptions longer than 18 hours will be calculated

Afterwards, analytically calculated reliability indices are used as “benchmark limits” for directly assessing risks of penalty

Considered Scenario

12

Considered Scenarios (Existing Networks & Future “Smart Grids”):

Existing Network Configurations & Functionalities (SC-1A/B): In accordance with Security of Supply Requirements (MV network have switching functionalities for transferring to alternative supply and for reconfiguration; otherwise large number of customers will be exposed to excessively long supply interruptions)

Considered Scenario

13

Considered Scenarios (Existing Networks & Future “Smart Grids”):

“Smart Grid” Scenarios (SC-6A/B): Represent functionalities available in future networks -- in this case automatic remote-controlled switching implemented in MV network (LV network is still protected only by the fuses)

Considered Scenario

14

Considered Scenarios (Existing Networks & Future “Smart Grids”):

Various Regulator Requirements (SC 2A/2B to SC-5A/5B): Used ONLY for analytical assessment and formulation of corresponding limits and thresholds against which risks of penalties will be assessed after probabilistic results are obtained

Results: Analytical Assessment15

MV Network Only MV Network & LV Equivalent

Results: System Assessment

Significant increase of CAIDI value is indicated for Scenario SC-6A/6B,when “smart grid“ automatic switching is applied… (?!)

CAIDI (MV Network) CAIDI (MV Network & LV Equivalent)

0 200 400 600 800 1000 1200 1400

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

SC-1A Analytical Mean=8.953SC-6A Analytical Mean=40.295

(for mean

, mean

and mean load)

CA

IDI

hours/customer interruption

SC-1A (MCS Mean=7.807) SC-6A (MCS Mean=47.326)

0 5 10 15 20 25

0.0

0.2

0.4

0.6

0.8

limit SC-3ARisk=7.4% (SC-1A)Risk=9.8% (SC-6A)

limit SC-2ARisk=7.2% (SC-1A)Risk=9.7% (SC-6A)

0 20 40 60 80 1000.00008

0.00010

0.00012

0.00014

0.00016

0.00018

0.00020

0.00022

0.00024

0.00026

SC-1B Analytical Mean=14.732SC-6B Analytical Mean=39.488

(for mean

, mean

and mean load)

limit SC-3BRisk=81.4% (SC-1B)Risk=100% (SC-6B)

limit SC-2BRisk=49.8% (SC-1B)Risk=100% (SC-6B)

CAID

I (PD

F)

hours/customer interruption

SC-1B (MCS Mean=15.487) SC-6B (MCS Mean=41.575)

Results: System AssessmentSAIFI (MV Network) SAIFI (MV Network & LV Equivalent)

All faults previously cleared after 15min or 3 hours are in SC-1A/1B resulting inshort interruptions (due to <3min automatic switching).

Corresponding supply interruptions are no longer contributing to the averageinterruption duration (resulting in a higher risk of penalty… still, number of faultsreduced in SC-6A/6B

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

SC-1A Analytical Mean=0.172SC-6A Analytical Mean=0.108

(for mean

, mean

and mean load)

SA

IFI (P

DF

)

long interruption/customer/year

SC-1A (MCS Mean=0.140) SC-6A (MCS Mean=0.059)

0.0 0.1 0.2 0.3 0.4

0.0

0.2

0.4

0.6

0.8

limit 1 interruptionRisk=3.9% (SC-1A)Risk=0.8% (SC-6A)

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

SC-1B Analytical Mean=0.0066SC-6B Analytical Mean=0.0063

(for mean

, mean

and mean load)

limit 1 interruptionRisk=73.8% (SC-1B)Risk=68.6% (SC-6B)

SAIF

I (PD

F)long interruption/customer/year

SC-1B (MCS Mean=0.0064) SC-6B (MCS Mean=0.0059)

Results: Customer Assessment

0 50 100 150 200 250 300 350

0.0

0.2

0.4

0.6

0.8

CAID

I (PD

F)

hours/customer interruption

SC-1A Cust 1 (MCS Mean=4.499) SC-1A Cust 8 (MCS Mean=4.1817)

0 4 8 12 16 200.0

0.2

0.4

0.6

0.8

limit SC-3ARisk=6.4% (Cust 1)Risk=5.7% (Cust 8)

limit SC-2ARisk=5.9% (Cust 1)Risk=5.1% (Cust 8)

SAIFI (SC-1A) CAIDI (SC-1A)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.2

0.4

0.6

0.8limit 1 interruptionRisk=2.7% (Cust 1)Risk=6.9% (Cust 8)

LI (P

DF)

long interruption

SC-1A Cust 1 (MCS Mean=0.067) SC-6A Cust 8 (MCS Mean=0.207)

Results: Customer AssessmentSAIFI (SC-1B) CAIDI (SC-1B)

0 20 40 60 80 100

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

limit SC-3BRisk=70.8% (Cust 1)Risk=72.6% (Cust 8)

limit SC-2BRisk=41.9% (Cust 1)Risk=41.3% (Cust 8)

CAID

I (PD

F)

hours/customer interruption

SC-1B Cust 1 (MCS Mean=16.0916) SC-1B Cust 8 (MCS Mean=15.1101)

0 1 2 3 4 5

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

limit 1 interruptionRisk=57.6% (Cust 1)Risk=65.4% (Cust 8)

LI (P

DF)

long interruption

SC-1B Cust 1 (MCS Mean=1.1375) SC-1B Cust 8 (MCS Mean=1.2720)

Results: Customer Assessment

0 200 400 600 800 1000 1200 1400

0.0

0.2

0.4

0.6

0.8

1.0

CAI

DI (

PDF)

hours/customer interruption

SC-6A Cust 1 (MCS Mean=18.8242) SC-6A Cust 8 (MCS Mean=13.0869)

0 4 8 12 16 200.0

0.2

0.4

0.6

0.8

1.0

limit SC-3ARisk=7.7% (Cust 1)Risk=5.8% (Cust 8)

limit SC-2ARisk=7.5% (Cust 1)Risk=5.4% (Cust 8)

SAIFI (SC-6A) CAIDI (SC-6A)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.2

0.4

0.6

0.8

1.0limit 1 interruptionRisk=0.3% (Cust 1)Risk=1.4% (Cust 8)

LI (P

DF)

long interruption

SC-6A Cust 1 (MCS Mean=0.0268) SC-6A Cust 8 (MCS Mean=0.0829)

Results: Customer Assessment

0 50 100 150 200 250 300

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

limit SC-3BRisk=82.6% (Cust 1)Risk=86.0% (Cust 8)

limit SC-2BRisk=80.2% (Cust 1)Risk=83.9% (Cust 8)

CAID

I (PD

F)

hours/customer interruption

SC-6B Cust 1 (MCS Mean=41.7844) SC-6B Cust 8 (MCS Mean=40.7858)

0 4 8 12 16 200.000

0.001

0.002

0.003

0.004

SAIFI (SC-6B) CAIDI (SC-6B)

0 1 2 3 4 5

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

limit 1 interruptionRisk=56.4% (Cust 1)Risk=58.7% (Cust 8)

LI (P

DF)

long interruption

SC-6B Cust 1 (MCS Mean=1.1113) SC-6B Cust 8 (MCS Mean=1.1557)

Risk Results

SC-1A (%) SC-6A (%) SC-1B (%) SC-6B (%)

Limit SC-2A/2B (GSP-UK) 0.28 0.08 36.8 68.6

Limit SC-3A/3B (GSP-Italy) 0.28 0.08 60.1 68.6

SC-1A (%)

SC-6A (%)

SC-1B (%)

SC-6B (%)

SC-1A (%)

SC-6A (%)

SC-1B (%)

SC-6B (%)

Customer 1 8 1 8 1 8 1 8

Limit SC-2A/2B (GSP-UK)

0.16 0.35 0.02 0.07 24.1 27.0 45.2 49.2

Limit SC-3A/3B (GSP-Italy)

0.17 0.39 0.02 0.08 40.8 47.5 46.6 50.5

System Risk’s

Customer Risk’s

THANKS!

Questions?

Mohd Ikhwan Muhammad RidzuanDr Sasa DjokicThe University of Edinburgh, UKm.muhammad-ridzuan@ed.ac.uk