Integrating Smart Transformers (SST) Into Distribution...

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Shaban Awili

December 2015

by

Integrating Smart Transformers (SST) Into

Distribution Substations

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Agenda

SST Research Motivation

Smart Transformer Technology Overview

System Integration Requirement

Impact on Distribution Substation

Cost Implications

System-oriented analysis summary

Identify

(SST) Advantages

Understand

(SST) Challenges

Develop

Comparison Framework

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Transmission HV Distribution MV Distribution LV

The Inevitable Change

“Our aim is that by 2027

we will have an activeElectricity Network That Maximises Renewables Usage” Said John Byrne

ESB

CONSUMER

USAGE

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The Smart iFuture

Smart Transformer

Add Functions Add Benefits

Potential Issues

Consumer ControlAdd Control

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“It is a box that can take energy in any form – it doesn’t care whether it is AC or DC – and it will provide energy on the secondary side with very few losses and to the

specifications set by the client.” By Dr: Aedan Kernan

Smart Transformer Overview

AC-DC Rectifier

Converts HV-AC (LF)

into HV-DC voltage

Dual Active Bridge (DAB)

Uses HF Transformer &

Switches to Convert HV-DC

into LV-DC voltage

DC-AC Inverter Converts

LV-DC into

LV-AC (LF) voltage

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SST Components/Applications

Source: http://www.marketsandmarkets.com/PressReleases/solid-transformer.asp

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SST Based Distribution System

B

E

C

DCL

CL A

F

LOAD DRER DESD

REL REL

REL REL

HV/MV (SST)

Based Substation

MV/LV (SST)

Based Substation

SST

SS

TS

ST

SST

10 kV

10 kV

400V

38 kV

Section3

Section2

Section1

FID FID

FID

RE

LR

EL

FID

FREEDM system

RE

LR

EL

REL

Distributed Renewable Energy

Resources (DRERs)

Distributed Energy Storage

Devices (DESDs)

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A

F

SST Fault Scenarios

B

E

C

DCL

CL

LOAD DRER DESD

REL REL

REL REL

SST

SS

TS

ST

SST

10 kV

10 kV

400V

38 kV

Section3

Section2

Section1

FID FID

Voltage below 0.8 Pu

IGBTs contained

in the SST

rectifier are blocked

Current is limited to

2 pu at

Terminals

SST is removed

by the Under

Voltage Protection

Current in Ter C

and D Does not

Exceed Maximum

current

FID FID

The over current

does not occur on

the primary

side of the SST

DRER/DESD keep

feeding the load

as backup

RE

LR

EL

RE

LR

EL

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Overloading Capabilities (LFT)

IEC 60076-7 Loading Guide

IEC 60076-5, Specifies The required short-circuit current withstand duration to be 2s.

Normal Cyclic Loading

� A higher ambient temperature or a higher than rated load current is applied during part of the cycle.

� 100 % for normal operation load

� Current (p.u.) up to 1,5

� Top-oil temperature 105 (oC)

� Hot-spot temperature 140 (oC)

Long–Time Emergency Cyclic Loading

� Loading resulting from the prolonged outage of some system elements that will not be reconnected before a steady state.

� 150 % for temporary overload

� Current (p.u.) 1,5



Short-Time Emergency Loading

� Unusually heavy loading due to the occurrence of one or more unlikely events which seriously disturb normal system loading.

� 180% for temporary half hour overload

� Current (p.u.) 1,8



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Overloading Capabilities (SST)

The power electronics components reduces the overload capability during load peaks.

The control action could provide a solution tothe overloading problem during the transients faults

The SST higher realization costs do not allow to oversize

In contrast with the grid components requirement of bearing currents higher than the rated values for

longer periods.

The SST needs new procedures for dealing with the over loading

conditions

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Overloading Control Concept (SST)

Photovoltaic (PV) plant equipped with a Battery Energy Storage System (BESS).

The BESS contributes to limit the power fluctuation in the feeder.

Manage a possible overload without derating the SST.

This will reduce the current and enhances the SST security against the

overload situation.

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Overloading Capabilities (SST)

Concept of the Coordinated Frequency and Voltage Overload Control.

Voltage and frequency of the master controller are set to nominal values (OS I).

The Master controller changes the frequency thought the DG droop controller (OS II).

After 35s Insufficient power contribution is After 35s Insufficient power contribution is reached and DG is not sufficient to control

frequency.

Master controller starts changing the voltage level at LV terminal of SST

The transformer overload is avoided for total of 60 sec (OS III).

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Impact on Substation Design (Physical Design)

(LFT) Fire Protection Transformer Design consideration

Table 16 : IEC 61936-1 2002 Recommendations for separation distancesbetween outdoor transformer and buildings

Transformer

Type

Liquid

Volume (l)

To

Other Transformers or non

Combustible Building

Surfaces [m]

To

Combustible

Building

Surfaces [m]

Oil Insulated

Transformers

> 2,000 <

20,0005 10

ABB 10 MVA 6,156 5 10

Horizontal Separation (a)[m]

Vertical Separation (b)[m]

5 15.2

5m

5m

5m 5m

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Impact on Substation Design (Physical Design)

(LFT) Transformer Substation Layout

10 MVA LFT

18%Potential

Reduction

SubstationArea m2

(LFT) Original Area

m2

(LFT) clearance Area

m2

(SST) Required Area

m2

PotentialArea

Reduction m2

1500 12 302 6 290

Reduction Oil

System Size

In Volume

Up to50% SST

ReductionIn Volume

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Cost Implications (LFT)

Total ownership cost consist of several components:

� Purchase price

� The Installation Costs

� Value of the Energy Losses

� Maintenance Costs

� Decommissioning Costs

Life Cycle Cost Breakdown

Factors A, B (€/kW), that depend on transformer type, size, loading conditions, as well as cost of capital, energy market

forecasts, expected transformer life.

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Cost Implications (SST)

Costs are estimated by means of component cost models for high-volume production

� Approximately factor of five more

expensive purchasing price.

� Produces roughly two to three

times higher losses.

� It offers reduction in the footprint,

weight and volume.

� It eliminates all associated costs

with using oil.

� Offers savings in the civil, transport

and installation costs.

� TOC will be higher due to the

higher purchasing price and higher

losses.

Weight Breakdown Material Cost Breakdown

“Solid State Transformer Market worth $204.3 Million by 2020” MarketsandMarkets : Market Research Consulting Firm

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SST System Benefits

Unlike the conventional (LFT) the (SST) offers additional system benefits that should be

considered when comparing to (LFT)

Universal

Fault Isolation

Instantaneous Voltage Regulations

Integrates Energy Storage

Actively Change Power Characteristics

Improve Power Quality

Provide DC Power

Provides ability to utilise input or output in AC or DC power.

Protects the load from power supply disturbances

Eliminates the tap changer requirement

Provides backup and reduces outages length

Control voltage and frequency levels will reduce the system losses

Provide reactive power compensation and system harmonic filtering

In substations it could be used to feed control equipment or to feed DC micro grid

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Summary

Identify

(SST) Advantages

Understand

(SST) Challenges

Develop

Comparison Framework

� Flexibility,

� Intelligence / Controllability

� Significant Potential in Smart Grid applications

� Reduction in Footprint

� Eliminating Fire Hazardous and the use of oil.

� Protection Integration Requirement

� Overloading Capability

� Additional losses implications

� New Asset Reliability

� LFT Represents a truly Experienced Competitor to (SST)

� Functionality

� Reliability

� Size, Wight and Volume

� Efficiency / Cost

� SST can only be judged in the context of a given application

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So What Shall we Do ?

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Any Questions

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Irishtimes.com, 'Engineers Ireland: Smart power to revolutionise future use of electricity', 2014. [Online]. Available:

http://www.irishtimes.com/sponsored/engineers-ireland-smart-power-to-revolutionise-future-use-of-electricity-1.1951236. [Accessed: 27- Nov-

2015].

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Smartgrid_Roadmap, 2015. [Online]. Available: http://www.seai.ie/Publications/Statistics_Publications/SEAI_2050_Energy_Roadmaps/Smartgrid_Roadmap.pdf. [Accessed: 27- Nov-2015].

Leonardo-energy.org, 'Cost-competitive solid-state distribution transformers online within two years | Leonardo ENERGY', 2015. [Online]. Available: http://www.leonardo-energy.org/blog/cost-competitive-solid-state-distribution-transformers-online-within-two-years. [Accessed: 27- Nov- 2015].

P. Tatcho, H. Li, Y. Jiang and L. Qi, 'A Novel Hierarchical Section Protection Based on the Solid State Transformer for the Future Renewable Electric Energy Delivery and Management (FREEDM) System', IEEE Trans. Smart Grid, vol. 4, no. 2, pp. 1096-1104, 2013.

De Carne, G.; Buticchi, G.; Liserre, M.; Marinakis, P.; Vournas, C., "Coordinated frequency and Voltage Overload Control of Smart Transformers," in PowerTech, 2015 IEEE Eindhoven , vol., no., pp.1-5, June 29 2015-July 2 2015

Huber, J.E.; Kolar, J.W., "Volume/weight/cost comparison of a 1MVA 10 kV/400 V solid-state against a conventional low-frequency distribution transformer," in Energy Conversion Congress and Exposition (ECCE), 2014 IEEE , vol., no., pp.4545-4552, 14-18 Sept. 2014

2015. [Online]. Available: http://static.mimaterials.com/midel/documents/sales/Guide_for_Transformer_Fire_Safety_Practices.pdf. [Accessed: 27- Nov- 2015].

2015. [Online]. Available: http://www02.abb.com/global/coabb/coabb051.nsf/0/8aa3946a6ad8e7c6c12577880053e1d8/$file/ABB+SPT+Transformers+-+Customer+Value+Proposition.pdf. [Accessed: 27- Nov- 2015].

2015. [Online]. Available: http://Solid State Transformer Market worth $204.3 Million by 2020. [Accessed: 27- Nov- 2015].

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References

Integrating Smart Transformers (SST) Into Distribution...

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