study the impact of connection of riyadh metro on the grid

Study the Impact of Connection of Riyadh

Metro on the Grid Stability and Power

Quality

EHV Network Planning Department

Overview

9051 NW_S1

9053 NE_S3

9054 SE_S4

9052 SW_S2

Riyadh Metro Substations

L1,L4,L2

Main Backup L4,L5,L6

L6,L4,L2, L5

Main Backup

L1,L4,L2

L3,L6

Main Backup

L1,L3,L2,L5

L1,L3,L5

Main Backup

L3,L6

L6 = 37 MVA

L1 = 128 MVA

L2 = 80 MVA

L3 = 98 MVA

L4 = 70 MVA

L5 = 81 MVA

The Total Load

is 494 MVA

2017 COA Network

Riyadh Metro Substations

Power Quality Study

Power Quality Measurements

Flicker Measurements

Check existing flicker levels on the transmission system are within SEC grid code limits

Harmonic Distortion Measurements

Check that existing harmonic distortions on transmission system are within SEC grid code limits

Voltage Unbalance Measurements

Check that existing unbalance on transmission system are within SEC grid code limits

In most cases, measurements were taken across 3 phases using a 3-phase wound voltage transformer

At Al Fakriyah and Al Mursalat, there was no access to this equipment so measurements were taken on a 1-phase voltage

transformer








Pst and Plt in Grid Code requirements are 0.8 and 0.6 respectively

Ro

le








The Voltage Unbalance shall be below 1% according to Saudi Grid Code

Measurements as expected (0.2% to 0.4%) for such a

strong system

The unbalance reported relates to the negative

sequence component.

Ro

le








Voltages should continually be within ±5%

The ±10% criterion is only applicable if it lasts for 30 minutes or less Ro

le

• Where possible the phase voltages are shown within the +5% levels

and, except Al Fakhriyah all recordings are within that limit.

• The recordings at Al Fakhriyah fall within the +5 to +10% band for

more than 30 minutes continuously. This effect is more pronounced

during night time.

• This is a issue which we recommend needs further investigation to

establish the root cause







Total Harmonic Distortion (THD) shall be below 1.5%

The Individual Harmonic limit is 1%


Ro

le

(1) THD is calculated based on 𝑉ℎℎ=50ℎ=2 for harmonic order h =2 to 50

HD

HD

HD








• Almost all measured values were within individual

harmonic limit of Saudi Grid Code

• The exception was the 5th harmonic at Al Mursalat

(which measured 1.065%)

• The measurements taken were measured over 3

days

• Theoretically, if measured over 1 week, the level would be under 1%

• The same effects have been noted in recordings made at Qurtobah, however the levels are not as high

• The level at Al Mursalat are not thought to be significant as; i) The cyclic nature of the recorded distortion and ii)

The mechanism harmonics affect various system plant items

Power Quality Studies and Results Voltage Fluctuation (Flicker)

Short Circuit Delta V Combined Pst

Methodology

Worst Plt

• For a 1 second repetition to produce a short term severity factors (Pst) value of 0.5, the voltage fluctuation requires is

0.4%. This equation can be used to linearly scale the resultant Pst

• All measurements are well below 0.1 level but for the purposes of the study to provide more meaningful results, a

value of 0.1 has been used as the background

• The worst case long term severity factor (PIT) was calculated based on 12 consecutive PST values. This is a very

pessimistic calculation and therefore demonstrates that the system can handle these worst case scenarios

𝑃𝐼𝑇 = 𝑃𝑆𝑇

Where; S is Minimum Short Circuit Level Pstbck is the background flicker M is the load step in kVA Pstnew is due to the metro load

Power Quality Studies and Results Voltage Fluctuation (Flicker)

• All short term severity factor results are below the limit

of 0.6 specified in the Saudi Grid Code

• This logic was applied to the long term severity factor

which results were also found to be well below the

limits prescribed by the Saudi Grid Code

• Therefore it can be concluded that the addition of the

new metro load onto the transmission system should

not cause any voltage fluctuations or flicker

Power Quality Studies and Results Harmonic Distortion

• All the imported PSS/E models are refined in Power Factory for the network elements

• The harmonic current injections for all three packages provided by ADA were individually modelled in PF at the

designated 33kV traction busbars for all the injections. The harmonic Norton equivalent injections provided for each of

the packages at the designated 33kV busbar were represented as harmonic Thevenin equivalents for all the injected

harmonics as input into the PF harmonic source model. For example, Package 1 injection at 9051 is modelled and

shown as “Vth P1@9051” in the figure.

• Harmonic load flow runs are then conducted for all the operational conditions as described in the below Tables and

tabulated results for the considered 380kV busbars are exported to excel spreadsheet after each run for analysis.

Saudi Grid Code compliance studies – 1

Harmonic studies with background considered – 2

Methodology


• All the imported PSS/E models are refined in Power Factory for the network elements

• The harmonic current injections for all three packages provided by ADA were individually modelled in PF at the

designated 33kV traction busbars for all the injections. The harmonic Norton equivalent injections provided for each of

the packages at the designated 33kV busbar were represented as harmonic Thevenin equivalents for all the injected

harmonics as input into the PF harmonic source model. For example, Package 1 injection at 9051 is modelled and

shown as “Vth P1@9051” in the figure.

• Harmonic load flow runs are then conducted for all the operational conditions as described in the below Tables and

tabulated results for the considered 380kV busbars are exported to excel spreadsheet after each run for analysis.

Harmonic mitigation studies to resolve Saudi

Grid Code non-compliance – 3 Harmonic studies using mitigation solutions

with background considered – 4

Methodology


• The harmonic load flows were also extended to obtain harmonic voltage distortions on the Metro 33kV busbars,

although not part of SEC transmission system.

• Harmonic studies were also studied using measured background levels to consider impact on the new traction sites.

These background levels were modelled in PF as voltage sources from the selected measurement sites in the SEC PF

model using their 95th percentile values. Therefore, the total distortions from the assumed sources from SEC system

(measured background) and the traction loads are calculated by PF as a vector summation.

Methodology


For the 33kV busbars at distribution level, there was non-compliance for the 7th for both intact and single worst degraded cases for the individual and THD level of 2%(odd) and 3% respectively and approaching 10% at 190511

For the 33kV busbars at distribution level, there was non-compliance for the 7th for both intact and single worst degraded cases for the individual and THD level of 2%(odd) and 3% respectively and at worst of over 10% at 190511

200 kVAr 7th single tuned (ST) connected at 33kV at 19051 NW_S1, 19053 NE_S3 and 19054 SE_S4 brought the harmonic levels at 33kV to well within Grid Code

With the proposed mitigation solutions used to resolve the non-compliance issues, all issues at 33kV still remained compliant with the background harmonic levels

2017 M

itig

ati

on

Mit

igati

on

Harmonic

studies With

background


For the 33kV busbars at distribution level, there was non-compliance for the 5th and 7th for both intact and single worst degraded cases for the individual and THD level of 2% (odd) and 3% respectively and marginally exceeding 2% and approaching 5% for the 5th and 7th respectively

For the 33kV busbars at distribution level, there was non-compliance for the 7th for both intact and single worst degraded cases for the individual and THD level of 2%(odd) and 3% respectively and at worst of over 5% at 190511 and for one case of outage 9052 with 10Mvar capacitors switched IN also resulted in the 5th at 190541 also marginally exceeding 2%.

200 kVAr 7th single tuned (ST) connected at 33kV at 19051 NW_S1, 19053 NE_S3 and 19054 SE_S4 and;

200 kVAr 5th single tuned (ST) also connected at 19054 SE_S4.


2020 M

itig

ati

on

Mit

igati

on

Harmonic

studies With

background


For the 33kV busbars at distribution level, there was non-compliance for the 7th for both intact and single worst degraded cases for the individual and THD level of 2%(odd) and 3% respectively and approaching 10% at 190511

For the 33kV busbars at distribution level, there was non-compliance for the 7th for both intact and single worst degraded cases for the individual and THD level of 2%(odd) and 3% respectively and at worst of over 10% at 190511

200 kVAr 7th single tuned (ST) connected at 33kV at 19051 NW_S1, 19053 NE_S3 and 19054 SE_S4 and;

200 kVAr 5th single tuned (ST) also connected at 19054 SE_S4.


2024 M

itig

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on

Mit

igati

on

Harmonic

studies With

background


A solution was worked in the form of four individual single tuned filters:

One 7th single tuned filter at 33kV at 19051


Two single tuned filters at 33kV at 19054 at 5th and the 7th

Solution

Power Stability Study

Scope and Objectives

• Thermal rating of lines, cables and transformers.

• Voltage levels against SEC system planning criteria.

• Reinforcement requirements. Load Flow Studies

• Short circuit levels with metro load.

• Rating of the switchgear capability to interrupt fault currents. Short Circuit Studies

• Transient voltage stability .

• Motor stalling.

• Three-phase and single-phase faults.

Transient Stability Studies

System conditions studied before and after the connection of the metro loads to

distinguish issues caused by the connection of the metro loads

Traction Load Model

A User-Written load model was developed to allow the dynamic behaviour of the traction loads for the

4 feeder stations to be specified for the PSS/E dynamic studies.

BUSID ‘USRLOD’ IL ‘MODEL NAME’ IC IT NI NC NS NV NRI DATA LIST/

IL – load identifier or * to specify all loads at this bus bar with ‘BUSID’

IC – specify ‘0’ for model call from CONET (i.e. load related)

IT – specify ‘1’ for current injection model (before IFLAG test in subroutine CONET)

NI – number of ICONs

NC – number of CONs

NS – number of STATEs

NV – number of VARs

NRI – number of additional reserved ICONs

Traction Load Model

Example entry at a SEC 33kV traction bus bar for user load model:

T1 T2 T3 T4 P1 P2 P3 P4 PF1 PF2 PF3 PF4

190511 ‘USRLOD’ 10 ‘SECTBL’ 12 1 0 12 0 0 0 3 4 5 6 25 30 35 25 0.95 0.95 0.95 0.95/

where:

T1, T2, T3, T4 is the time in seconds where P MW changes,

P1, P2, P3, P4 is the traction load in MW corresponding to simulation times T1, T2, T3, T4,

Followed by the four corresponding power factors PF1, PF2, PF3, PF4 for the switched P MW respectively.

The power factor can be user specified for all switched P MW loads to reflect the

corresponding Q Mvar part of the loads where default is at unity power factor

Traction Load Model

Graphical step change P MW that can be specified for the user load

model illustrated for the example given.

Traction Load Model

DYRE file showing user defined traction load specification

2017 Studies Results

Load flow studies

- The metro loads do not have a significant impact on the thermal loading of the circuits.

- Slight overloading of 3% on the 380kV/33kV transformers at GS 9053 during the complete outage of GS9051.

- No voltage issue observed from the studies due to the metro load connections.

Short circuit studies

- No Short circuit fault levels exceed the designated breaker ratings.

- The switchgear is still within sufficient margin of its assumed 63kA rating.

Transient stability studies

- No stability issues observed.

- Adequate power damping following disturbance.

- Voltage recovered to within SEC criteria for the affected bus bars.


Load flow studies

- The metro loads do not have a significant impact on the thermal loading of the circuits.








- Repeated studies for faults at 380kV and 132kV bus bars did not identify any issues of induction motors stalling.


Load flow studies






- Largest increase in fault levels from 2020 to 2024 (71% to 83.3% and 67.1% to 80.5% for 1Q-F at 9051 and 9054.



- Adequate power damping following disturbance.

- Voltage recovered to within SEC criteria for the affected bus bars.

Without Metro Traction Load

After Metro Traction Load Steps

Transient Stability

Results Comparison

Transient Stability Results Comparison

Conclusions and Recommendations

• During the outage of any supply point, transformer loading exceeds the 80MVA ONAF rating. Hence during such times

the transformers will need to be operated at the 100MVA OFAF rating.

• Short-circuit studies did not show any breach of the rated switchgear break capability and hence no further action is

recommended.

• Stability studies indicated that the system is functioning within the technical performance criteria and that the addition of

metro load will not affect the stability of the system and hence no further action is recommended in this regard.

• All measured 95th percentile values of Pst and Plt are well below the Saudi Grid Code requirements.

• The 95th percentile voltage unbalance measurements measured are shown to be below the Saudi Gird Code

requirements of 1%.

• The 95th percentile values of the Total Harmonic Distortion as measured are well within the allowable limit of 1.5%.

Conclusions

• Background and combined values of short and long term flicker are all well within the levels prescribed by the Saudi

Grid Code. An assessment has concluded that the addition of the new metro load onto the transmission system should

not cause any voltage fluctuations or flicker beyond the acceptable levels prescribed in the SEC Grid Code.

• The results of the harmonic voltage distortion studies indicate that the levels calculated at the 380kV and 132kV

busbars are compliant with the levels prescribed in the Saudi Grid Code. As per the Saudi Grid Code, these limits are

1.5% for Total Harmonic Distortion (THD) and 1% for the individual harmonics. It is noted that when harmonic

distortions are assessed to include effects of background harmonics, the new 380kV traction substations are still within

the planning levels of Saudi Grid Code.

• Investigations at 33kV nodes indicated that the 5th and the 7th harmonic orders are well above the allowable individual

harmonic distortion level prescribed in the SEC Distribution Code. These results are based on all individual injection of

harmonic currents from all three metro developer packages occurring simultaneously and were studied for normal and

single worst degraded metro operation at 33kV. A solution was worked in the form of four individual single tuned filters:



Two single tuned filters at 33kV at 19054 at 5th and the 7th

Conclusions

• With respect to the individual phase voltage exceeding the +5% criterion on a continuous basis, we would

recommend extended measurements and investigation of this overvoltage recording in order to establish the root

cause(s). This should then be supplemented with comprehensive risk assessments in terms of SEC asset

management policies taking into account insulation requirements.

• With respect to marginal non-compliance of the 5th harmonic at Al Mursalat, we highly recommend that revised

harmonic distortion levels at Al Mursalat are established following energisation of the metro load from 9053 along

with the new cable circuit planned in the vicinity. This is because Al Mursalat will eventually be connected to the

new grid supply point 9053 and on route to Qurtobah. These changes are likely to introduce new resonances or

shift existing resonances and hence the new measurements may show a different picture. An additional immediate

action is to investigate the reason behind the magnification observed at the level for the 5th harmonic at Al Mursalat

and to a certain extent at Qurtobah so that appropriate decisions in terms of mitigation requirements or measures

can be taken and consider measurements over a longer period.

• With respect to the breaches identified at 33kV, the proposed solution can be implemented without further studies.

However, we would recommend more detailed studies in order to optimise the choice and location of passive filters.

This detailed study should also look into the lines of responsibility in terms of who should implement the necessary

mitigation.

Recommendations

Thank you

study the impact of connection of riyadh metro on the grid

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