SAUDI ELECTRICITY COMPANY """1 e j - &a

6. Horizontal clearance between GIB and GIs buildinglany nearby building wall shall be minimum three (3) meters.

7. The GIB route shall not obstruct easy access to GIs and control buildings and shall not obstruct movement of crane, equipments including HV test equipments for maintenance work.

8. For the maintenance of GIB of one circuit, only that circuit shall be isolated.

9. CONTRACTOR shall provide the GlSlXLPE Cable connection interface drawings and details of cable compartments in order to enable the cable terminations of the XLPE Cables in future, which has to be terminated to the then existing cable compartments.

The drawings and details should contain all the parts supplied by the GIS

8 ,4

, I

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Manufacturer of the cable compartment for the connection between GIs and power cables according to IEC 62271-209.

(vi) Each removable b i i Seaion is to be connected via~,compression ioints nr other Suitable means such that it would be possib!e to remove an bus.-section ! wittiout having to disassemble the bus sections immediately ahe d and Behind the concerned section.

(vii) The 380 kV, XLPE, 3 x 1C 2500mm2 cable length between # 9008 and tt 9024 BSPs is 1 Okm.

4.06 INSULATION COORDINATION STUDY. PROCEDURES AND GUIDELINE

The objective of insulation coordination is to bring the insulation strengths of electrical equipment into the proper relationship with expected over voltages and with the characteristic of surge protective devices. Insulation Coordination is the process of determining the proper insulation levels of various components in a power system as well as their arrangements. The process is determined from the known characteristics of voltage surges and the characteristics of surge arresters.

/ r\ccordingly, the conclusion would be whether the insulation level IS adequate or some mitigation (usually surge arrestor installation) would be suggested. This is guide line for carrying out the above process in an accepted way by SEC. Please be aware on the following:

There are three basic elements to insulation coordination, which are:

1. Determining the over voltage stresses from the system. Over voltages have to be determined by system simulation using EMTDCIPSCAD software.

THIS DKAWING IS NOT Therefore, a close to the actual model of the system has to be build as TO BE USED @OR CONSTRUCTION OR explained below. A soft copy o f the cases studied has to be Submitted in

MATERWLT UNTU PSCAD format. Cases to be simulated are Present and Ultimate (Minimum

CERTIWIED AND DATED and Maximum)

FOR-EXPANSION OF NAFL (# 9008) 380kV ESP

g - - - REVISIONS

~ ~

DB*WNBY;

DATE: 20-08-2011

I > S DWLWING IS NOT BE USED POR

'CONSTRUCIION OR FOR ORDERING MATERMLS UNTIL CERTIFED AND DATED

JOB ORDER NO. t

>

SAUDI ELECTRICITY COMPANY v$l &id\ e j - 94& ;?;l~&l %*I

2 Knowing the strength of the insulation of specific equipment in the substation. The insulation criteria have to be fulfilled against all possible over voltages.

3. Selecting surge arrester ratings and locations, or other mitigation equipment or operating restrictions, to ensure the system-imposed over voltages do not exceed the insulation strength of the equipment including an appropriate protective margin.

Svstem Modelinq I I The first step in insulation coordination study is to build a detailed frequency dependent EMTDCIPSCAD simulation model that reflects the behavior o f the key system components. Such components are GIs, transmission line, cables, transformers, surge arrestors, reactors etc. A system equivalent reflects the rest of the system has to be modeled as well. Sensitivity for some uncertain parameters has to be adopted.

GIS. the model of GlSls has to be collected from the GIs manufacturer and it has to be a cable model.

. .. . ' . Transmission lines and &ables! SEC . ..... shall the'data fdr the +Z[iting

stations while the ongoing projects -data shall collect from the transmission line contractor. Frequency dependent model has to be consjdered far the analysis purposes.

Tower and take-off structure: Proper model has to be considered for the towers and take-off structures. Consider a varying tower footing resistance from 0 to 20 ohms regardless of measured value.

Svstem Eauivalent: two buses away from the GlSls of concern have to be modeled and system equivalent for ihe rest of the system is to b e collected from SEC.

V-l characteristics of the surge arrestor. I I I

The built system model should match the PSSE load flow and short circuit / \.." autput for verification before carrying out the simulation. I l

P.II the network elements required for over voltage analysis purposes shall be I

designed /modeled in detail and the designlmodeling criteria shall be supported by

I well-recognized literature and references.

I Over voltaae Simulations

1 To assess the insulation level of the svstem. the over voltaae stresses on the I equipment has to be known through simuktion.

-

I

1 The different types of over voltages that may occur on a power system and shall be s~mulated are:

Temporary over voltages.

[PTS - 11CR343- MGR IPAJ, AUGUST, 2011

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Switching over voltages (Statistical and Deterministic).

Fast transient (Lightning) over voltages.

Very fast transient over voltages.

Temvoraw Over voltaaes (TOV)

These may usually be short power frequency over voltages or weakly damped

REVISIONS

DmWNBY:

oscillatory voltages. Those are power frequency over voltages that last f o r more than a cycle and can last a number of seconds.

The main (but not restricted to) causes of these over voltages are:

Phase to Earth Faults: Single line to Ground, Double line to Ground, 3 Phase to Ground.

. .

DATE;

CKWOBY: Y \

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,.+" N? BY. / DATE: 20-08-2011

n t l s DRAUTNG 1s NOT TO BE USED FOR CONSTRUCTION OR BOP. ORDERmG MATERIALS UNTIL C E R T I ~ D AND DATED

JOB ORDER NO.

*

Load Rejection.

Resonance and Ferro Resonance.

o Ferranti Effect. . ~.. I

0 ' combination of temporary over voltage origins such as earth Iaui twi th load I

rejection.

Switchina Over voltaqes (Statistical and D e t e r m i n w

These surges are of short duration, irregular (or impulse form) and highly damped. Those are Over voltages arising from switching operations performed in the network as follows;

Transmission linelcable energization and re-energization,

Transformer energisation,

Faults and fault clearing,

/ c Load rejectionsi

Switching of inductive or capacitive currents, etc,.

Switching: (Slowfront) over voltages play a role in determining the energy duty of surge arresters and in the selection of required withstand voltages of equipment as well as the air gap insulation for transmission line towers. Statistical switching approach for different configuration has to be simulated where the actual closing time is statically chosen using a random-flat distribution within a one-cycle window. The pole span of the breaker is chosen to be 5 ms with 2.5 ms standard deviation. The switching over voltages is determined for 100-200 simulation. i

I..

The effects of such over voltages are o f great concern when the transmission voltage is greater than 300 kV. However, below 300 kV, some causes of these over voltages, that require simulation, are:

[PTS - 11CR343- MGR /PAJ, AUGUST, 201 1

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o*:e Lightning over voltages shall be studied to deter~rline the risk of equipment failure

LWK'DBY and therefore to select their required withstand level in relation to protective device configuration and tower earthing, and to evaluate line and station performance.

The two types of lightning have to be considered are direct stroke to the phase r N c W e a m G o e s r 1- I conductors and the back flashover. The magnitude of lightning curre t for'both the

cases shall be estimated using proper techniques and shall be explained. Consider a varving tower footing resistance from 0 to 20 ohms regardless of measured value.

SAUDI ELECTRICITY COMPANY 14491 &hidl fj - p 4 N

Resonance effects when switching transformer feeders, or cables and overhead lines.

Ferro resonance encountered on transformer feeder double circuits, when one circuit is switched out but the other parallel feeder remains energized.

Line energisation may cause switching surges especially at the remote end of the line that is being energised.

Liqhtninq Over voltaqes rFast-front Over voltaaes lFFOU

They are essentially produced by lightning strokes. Their magnitude is much larger than other kinds of over voltages. FFO are therefore critical for all voltage levels, and it is essential to mitigate them with protective devices, i.e. mainly surge arresters.

1 - 1 Very Fast Transient Over voltages (VFTO)

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VFTO are generated in GIs due to the breakdown across the contacts of discorlr~ector during a switching operation or line-to-ground fault. Very fast transients {VFT) in GIs can be divided into internal and external. Internal transients can produce over voltages between inner conductors and the encapsulation and external transients can cause stresses on secondary and adjacent equipments.

REVISIONS

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Internal Transients

..,,/~ur~es traveling throughout GIs and to other connected equipment are reflected and refracted at every transition point. As a consequence af multiple reflections and refractions, traveling voltages can increase above the original values and very high frequency oscillations occur. VFTO are characterized by their very fast rise-time, of the order of nanoseconds and followed by high-frequency oscillations of sevem! kHz to MHz. VFTO magnitude depends on the substation layout, the switching condition as well as the trapped charge on the open end of the GIs bus. Hence it is to be determined using simulation techniques.

1 DRAWING Lri NOT BE USED POR

External transients (Transient Enclosure Voltages (TEV)) 1 ,kmION POR ORDERMG MATERIALS UNTIL CERTIX'IEDAND DATED

An internally generated VFT propagates throughout the GIs and reaches the bushing where it causes a transient enclosure voltage and a traveling wave that propagates along the overhead transmission line. The transient enclosure voltages

- JOB ORDER NO.

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(TEV), also known as transient ground potential rise (TGPR), are short duration high voltage transients which appear on the enclosure of the GIs through the coupling of internal transients to enclosure at enclosure discontinuities. Determination of TEV and suggestion for mitigation of TEV is required.

D R A W B Y ,

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Insulation Coordination Criteria

The insulation coordination criteria are to be fulfilled against the severest over voltages of each type. The types of over voltages and the studies to be considered are: ('

Temporary over voltages (TOV): should not exceed the fundamental frequency withstand voltage for any equipment.

Switching over voltages: 98% out of the statistical switching for any switching operation should not exceed 80% of the BSL ( switching Impulse Withstand limit) . Lightning over voltages: for both direct stroke and back flashover events, the

, . maximum determined over voltage at any equipment should not exceed 80% of the BIL of that equipment. . .

.> II

1 . . .: . Very Fast Transient over ,voltages ( v ? T ~ ) : Internal transients and external ' i . .

transients (TEV) and its mitigation techniques.

In all cases, the surge arrestor measured energy absorption should be with the surge arrestor energy capabilitylclass.

I I Conclusion of the insulation coordination study I The insulation coordination conclusion has to be inline with SEC standard and fulfill the insulation criteria above. Such conclusion may recommend that:

The existing insulation is adequate and fulfills the criterla

There is a need for a surge arrestorlsurge arrestors of X class at X location GBnmm 1 , There is an operation restriction and controlled witching is needed

A suggested surge protection device other than surge arrestor

e-y* DATE: 20-08-2011

THIS DRAWING IS NOT TO BE USED POR CONSTRUCTION OR XOR ORDERmG MATERIAIS UNTIL CERTIFIED AND DATED

Ferro resonance analvsis and its mitiaation

Ferro resonance is a non-linear resonance phenomena occurring in a low loss electric circuit containing a non-linear inductance, capacitor and voltage sources. Power network is example of such an electrical circuit, where non-linear ~nductances are due to magnetizing impedances of power transformers, measurement inductive voltage transformers and capacitances are due to cables, Series capacitors etc. Hence, certain switching actions, operating conditions and a few system configurations may cause occurrence of Ferro resonances. Some examples of switching actions are transformer-switching, capacitor switching etc. Some of the configurationslconditions that may cause Ferro resonance are;

JOB ORDER NO

[PTS - 11CR343- MGR IPAJ. AUGUST. 201 1

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1. Transformer supplied through a long transmission line or cable with l ow short- circuit power,

2. Opening of one or two phases of a cable feeding the primary side o f a lightly loaded transformer.

3. Transformer energized through the grading capacitance of one or more open circuit breakers,

4. Transformer connected to a de-energized transmission line running in parallel with one or more energized lines

5. Energization of lightly loaded or unloaded transformers,

6. Transformer connected to a series compensated transmission line,

7. Transformers working with voltages very near the Knee point

8. Switching of CVTICCVT in the system,

9. Ungrounded transformer primary conne'ctions, ,:" ... .. -. . . . . . *. I , . r . : \ ~ A : , .

10. Cable damage and manual switching during construction of underground cable systems,

11. The use of single-phase switching devices on 3-phase systems,

A detailed s!udy is required to explore all the sources (not restricted to above conditions) of Ferro-resonance in a power system and to be explained in the repor?.

I - - - I . Ferro resonance Prediction

Ferro resonance is frequently accompanied by some of the symptoms described below.

,/ High permanent over voltages of differential mode (phase-to-phase) andlor common mode (phase-to-earth),

High permanent over currents,

High permanent distortions of voltage and current waveforms,

Displacement of the neutral point voltage,

I I Transformer heating (in no-load operation), I DRAWING IS NOT

POR ORDERmiG MATERIALS UNTIL CERTIFIED AND DATED

JOB ORDER NO. t Continuous, excessively loud noise in transformers and reactors. I Damage of electrical equipment (capacitor banks, VT, etc.) due to thermal effect or insulation breakdown. A characteristic symptom of VT destruction by Ferro resonance is a destroyed primary winding and an intact secondary winding.

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e l Apparent untimely tripping of protectiondevices.

Owing to the stochastic manner of Ferro resonance, detailed digital modeling of the system and computer simulations are required for the prediction of Ferro resonance occurrence. It is required to use frequency dependent complex model for the cable circuits incorporating the transpositions, cross-bonding etc. for the study.

Conclusion of the Ferro resonance analysis

The Ferro-resonance conclusion has to be in line with SEC standard. Such conclusion may recommend that:

List out the different sources of Ferro resonance in the power system and the mitigation methods to be adopted.

The magnitude and the time duration of the oscillations, which exist during the Ferro-resonance. The frequency of the oscillations shall also be provided in the conclusion.

9 Harmonic analysis to compute the magnitude of fundameqtal and other harmonic components in the current and voltage

of fundamental frequency as well as other harmonics. magnetizing current and voltage v~aveforms are signal

Advise for the protection of EHV and HV equipments in case of over voltages and Ferro-resonance.

**** END OF SECTION IV ****

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