Impact of Reactive Compensation on Ergon Energy’s LV Network, Research Proposal Example

Abstract

This paper analyses the different type of LV Networks in Ergon. It also critically reviews the importance of reactive power in the electricity network and the effects it has on PF. In the paper, there is also a basic tool developed for understanding and comparing the resistive rise and reactive benefit on different LV networks. There is a model of a series of networks that quantifies reactive power benefits under different LV network configurations. An economic comparison for reactive power has also been availed within the paper.

Background information

Reactive power is one of a class of non-energy power system operating needs collectively known as ancillary services. Other ancillary services include regulation, synchronized and non-synchronized reserves, and Black Start Service. Reactive power is unique among other ancillary services in that it must be delivered throughout the transmission system in close proximity to load centers.

Literature Review

Reactive power is provided by an array of generation and network devices, including generators, capacitors, synchronous condensers, static VAR compensators, and Static Synchronous Compensators (STATCOMs). Distributed energy devices also have the capability of producing reactive power and voltage support. Intuitively, there seems to be a good match between the requirement for reactive power supplies near load centers and the availability of distributed energy near or at customer loads.

Reactive power is essential for the sustenance voltage that has to be sustained for reliability of the system. According to research, When reactive power supply decrease voltage, as voltage decreases current has to increase to preserve power supplied, instigating the system to use up more reactive power and the voltage reduces even further.

LV networks vary layouts and designs vary according to the specific needs (extreme or maximum) voltage requirements of the given client. However, there are two main types of LV networks, the commercial or industrial development and the residential subdivisions. The industrial or commercial development are much more complex and are highly uncertain. This is attributed to the fact that precise information on the maximum requirements is scanty and there is need for the creation of an information database where all information pertaining to the activities of a given industry can be easily accessed.

The economic impacts of reactive power enhancement on a given system is substantial. Nonetheless, the availability of other sources of energy may nullify the economic viability of pursuing such an endeavour. Nonetheless his does not rule out the economic viability of executing such changes to an electricity supply system. This is because such a plan would increase equipment shelf life, on both the consumer side and the supply side.

The importance of reactive power cannot be understated. The effects on equipment, on the supply side and the consumer side are far too considerable to be ignored. Most notable is the fact that reactive power significantly reduces the incidences of power loss in transformers and power cables.

There is a need to develop a basic tool that can be used to measure and compare the resistive rise and reactive benefit on the different LV networks. This is essential in the determination of which layout is particularly suited and most efficient for a given client with regards to their maximum or extreme voltage needs.

Each and every LV network design is governed by its own design rules. These design rules are meant to give a standard guideline that ensures an efficient LV network that operates at optimum performance and capacity. When these design rules are flaunted, then there is a high risk of voltage drops and the eventual collapse of the functionality of the LV network. This creates even more risk to the equipment on both the supply side and the consumer side. This is because equipment will experience increased real power, without reactive power to counter, balance and sustain the voltage at reasonable levels.

Project Plan (Project Milestones)

The objective and milestones of this project are:

  • Review the types of LV Networks in Ergon, elements related to the network layouts, the requirements, typical values and extreme case across the network.
  • Review the importance of reactive power in the electricity network and the effects it has on PF, stability and protection.
  • Develop a basic tool for understanding and comparing resistive rise and reactive benefit on different LV networks.
  • Model a series of networks to quantify reactive power benefits under different LV network configurations.
  • Look into the economic comparison for reactive power

All the project milestones were realized by the completion of the project.

Since the project was executed in a low risk lab, there were no risks that were associated with the project at any given time. All the milestones did not entail any risks whatsoever.

LV NETWORKS

Types of LV Networks in Ergon

Ergon energy offers a wide range of LV networks. However, it is important to note that the types of network designs is limited to a number of factors that follow pre-set design rules designed to ensure maximum voltage output and sustenance of electricity supply to the customers.

The network design of the LV network at Ergon is limited by the following constraints:

  • The range of standard conductor sizes that Ergon possesses.
  • The controlled voltage parameters that have to be preserved at the customer’s terminals.

Note: it is important to note that the voltage calculations will be strictly associated with the distributed customers.  This means that a great deal of consideration is placed on the diversity, demand and unbalance, all of which vary according to the customer class.

Generally, Ergon has two types of LV network design layouts;

  1. Residential Subdivisions URD
  2. Industrial/Commercial Development

Residential Subdivisions URD

Typical Network Layout

The typical network arrangement for residential subdivision URD is a loop pillar plan as depicted in the figure below.

LOW VOLTAGE NETWORK DESIGN

From the supply pillar, a single-size mains cable (3ɸ-240mm2) is entwined to the supply pillar to create a circuit.in the distribution pillar, tee connections are made to other roadways.

On every other property boundary, pillars (cross-road and Supply) are placed on both road sides. They are placed together with a 3ɸ 16 mm2 Cu cable that connect the cross road pillars that are on the remote roadside to the supply pillars that are on the main’s cable roadside.

The client’s main is then linked via a fuse within the pillars on both roadsides.

Street lighting posts are supplied from the closest pillar through a cables that are fuse protected.

A Combined Fuse Switch (CFS) is employed to connect circuits of neighbouring substations.

Note: transfer capacity is not provided by that fact of the existence of linking pillars. This kind of facility is only designed for alternative supply, low capacity in times of light load for maintenance activities.

Low Voltage Network Design

  • Lighting posts connected to connecting pillars ought to be linked to the supply side on which the post is physically located
  • The extreme number of customers have to be connected to a circuit that voltage restrictions will permit
  • Circuits have to be radial
  • Service links must be balanced over the three phases, continuously along a circuit.
  • All services in a linking pillar ought to be connected to the same supply side of the pillar
  • One link via a switch per circuit should be provided to a circuit stemming from another transformer (where interconnection is solitarily probable to a circuit of the same transformer, then this is acceptable).

ADMD (URD)

The determination demand load of the potential customers that need electricity supply is vital for the design development of low voltage circuit supplying distributed clients. This is also vital for the determination of padmount substation requirements and the calculation of voltage drop.

An ADMD (after diversity maximum demand) is defined and then applied to all the clients within a given circuit. The ADMD adopted varies with varying climatic conditions, socio-economic conditions and the availability of alternative energies.

There exists design rules for conventional housing development depending on Ergon regional centres where there is availability of reticulated energies.

Mackay, North and Far North and (MK, NQ and FN)

  • ADMD = 5 kVA per Lot

Capricornia, Wide Bay and South West (CA, WB and SW)

  • ADMD = 4 kVA per Lot

Voltage Drop Calculations

The voltage range at the client’s terminal that is acceptable (usually located at the Ergon Pillars on the neighbouring property boundaries is usually:

  • 256 to 226 Volts ɸ-N, or;
  • 415/240 Volts ±6%

Note: voltage drops are compensated for in calculation purposes as a variation from nominal. For this reason, ADMD’s have been chosen to accommodate changes in demand.

Design Rules:

  • The volt drop on the distribution cable (from the distribution column to the customers’ stations in the cross-road pillar) is to be taken as 1%.
  • The volt drop on the mains cable must not exceed 5% (to the final distribution pillar).
  • Unbalance Factor 1.8
  • Volt Drop Confidence Factor 2.0
  • Standard Deviation = ADMD
  • TXF Confidence Factor 1.65
  • Cable Confidence Factor 2.0
  • Transformer Type – Low Impedance

INDUSTRIAL/ COMMERCIAL DEVELOPMENT

Network arrangement

When it comes renewal sites and new developments, there exist more diverse circumstances as compared to residential areas. For this reasons, there exist certain limitations of LV Networks that can be attributed to the unpredictable nature of this kind of development.

New Developments

The LV network design and layout that is employed in industrial/commercial developments is similar to the Loop Pillar system that is utilized for URD, with one notable difference, the supply pillars are employed on both roadsides. The extreme 3ɸ level of supply that a customer obtains from a supply pillar is usually 80 amps. This limit is effected by the fuse capacity that exists in the pillar.

In most scenarios, the 80 amp limit is found to be sufficient, not forgetting only 4 clients are able to experience that rate of supply when connected to the same circuit, subject to the voltage drop requirements being met.

The anticipated demand is used to match the cross road rating.

In the case where the estimated extreme demand of industrial or commercial client may exceed the fuse rating of a supply post, a pillar type-A should be utilized. This is done by linking the client to the load side of the CFS (Combined Fuse Switch) Unit and where the mains cable is looped in the post, these are linked back-to-back on the supply-side terminal.

The capacity of the CFS unit is 180A, however, if the client’s anticipated upper limit is above 140 amps (100kVA) then they will be supplied with one of the following:

  • dedicated circuits to the customer’s terminals from the substation.
  • a substation situated on the customers property

The latter is founded on the conjecture of the determined knowledge of the potential client’s extreme demand, however, in most cases this will not be true. There exists the high possibility that the cross road cables and pillars will need to be augmented. In the case where the agreed extreme may surpass 100kVA, Ergon Energy has a Constituted right to necessitate a pudmount substation site within the premises. This right ought to be executed in areas where provision of that supply dwindles.

Renewal Projects

In the renovation of commercial areas that exist, there are alterations in the amenity and/or purpose and subsequently, the electrical demand. This may create a wide range of issues and it is largely problematic to establish new sites or create substations at the preferred location.

The Distribution Cabinets that have been shown in the figure below, allow for distribution points to be created at the locations isolated from the given substation locations.  These cabinets are capable of facilitating up to 5-630 amp fuse strips. This is done for the distribution circuits that have isolators that control the incoming main.

The mains cable that feeds that distribution cabinet will have to be sized in order to meet the required voltage and demand. That standard arrangement is usually 2x240mm2 or 1x240mm2 mains.

ADMD (Industrial/Commercial)

The demand in these kind of developments vary and are irregular than the well know residential establishments. For design purposes, there lies a vital necessity to provide a guide that gives direction of the likely demand.

Voltage Drop Calculations

The voltage range at the client’s terminal that is acceptable (usually located at the Ergon Pillars on the neighbouring property boundaries is usually:

  • 415/240 Volts ± 6%, or

The design rules listed below will apply:

  • The volt drop on the service cable (from the main to the customers terminals) is to be taken as 1%
  • The volt drop on the mains cable must not exceed 5%
  • The volts at the transformer terminals are to be taken as 240 volts.

Note: voltage drops are compensated for in calculation purposes as a variation from nominal. For this reason, ADMD’s have been chosen to accommodate changes in demand.

Design Rules:

  • Standard Deviation = ADMD
  • Cable Confidence Factor 2.0
  • Unbalance Factor 1.8
  • TXF Confidence Factor 2.0
  • Volt Drop Confidence Factor 2.0

Note: this customer class is particularly hold a number of uncertainties, as such, there may be need for tweaking of certain facets to accommodate for this.

Cable Selection

Cables utilized in the LV Underground network can be branded as:

  • Mains cable
  • Cross road cable
  • Service cable

Mains Cable

Mains cables form the spine of the LV circuits looping amid distribution cabinets, supply pillars and substations. A single mains cable size is used – 240mm² Al, 4/C stranded sector cable, XLPE insulated PVC or NJ-PVC* sheathed.

The demand prerequisite from distribution Posts may require 2 x 240mm² Al, 4/C stranded sector cable, XLPE insulated PVC or NJ-PVC sheathed

Cross road Cable

Cross road cable links the mains cable in the supply pillar to the cross road pillar on the remote road side. The size of the cross road cable will be contingent on the application:

URD – 16mm² Cu, 4/C stranded circular cable, XLPE insulated PVC/NJ-PVC* sheathed

Commercial / Industrial

Supply over 75kVA – 240mm² Al, 4/C stranded sector cable, XLPE insulated PVC or NJ-PVC* sheathed

Supply up to 75kVA – 16mm² Cu, 4/C stranded circular cable, XLPE insulated PVC / NJ-PVC* sheathed.

Service Cables

Underground service cables link the supply network assets to the customer’s stations (mostly at the POS). This could be from underground or overhead network assets. In the loop column system this normally occurs in the columns and there is no service cable. The rating of the service cable has to be harmonized to the customer’s maximum demand.

POLE TOP SELECTION

In some circumstances underground LV cables will require to link to the overhead network as a cradle of supply or for connection purposes. Links may also be created for earthing reasons.

REACTIVE POWER

In order to improve system efficiency, reactive power is usually reduced. This is however only acceptable to some standard. If and when the system is purely capacitance or resistively, the electrical system may experience some technical problems. Alternating Current systems usually consume and/or supply two types of power, reactive power and real power.

Real power achieves expedient workload while the reactive power ultimately maintains the voltage that has to be sustained for reliability of the system. Notably, reactive power has an intense influence on power system’s security. This is because it influences the voltages through the whole system. Furthermore, loads such as motor loads need reactive power for the conversion of the flow of electrons to useful work. When reactive power is not sufficient within the system, voltage sags down and thus results in the inability to push the power demanded by loads through the power lines.

Importance of Reactive Power

Efficient operation of electrical power equipment is vital to avert any damage such as the overheating of motors and generators. Furthermore, it is important to ensure maintenance of the system’s ability to prevent and withstand voltage collapse, and also to diminish voltage collapse. In order for this to be realized, there is need for controls of voltage within the system.

When reactive power supply decrease voltage, as voltage decreases current has to increase to preserve power supplied, instigating the system to use up more reactive power and the voltage reduces even further. If the current upsurge is excessive, transmission lines go off line, overburdening other lines and possibly instigating cascading failures.

Reducing reactive power triggering voltage to decrease while increasing it initiating voltage to escalate. A voltage fall may be ensued when the system attempts to serve much more load than the voltage can sustain.

If and when the voltage dips too low, certain generators will disengage automatically to guard themselves. Voltage fall ensues when a surge in load or a reduced amount of transmission or generation facilities causes dipping voltage, which sources additional decrease in reactive power from line and capacitor charging, and even additional voltage reductions. If voltage decline lasts, these will source added components to trip, leading to loss of the load and more decline in voltage. The consequence in these total uncontrollable and progressive drops in voltage is that the system will be incapable of delivering the reactive power needed to supply the reactive power demands.

Necessity to Control Reactive and Voltage Power

Reactive Power management and voltage control are two facets of a solitary activity that both maintains consistency and expedites commercial trades along transmission networks.

On an AC (alternating current) power system, voltage is regulated by achieving absorption and production of reactive power.

The control of voltage and management of reactive power is important for the three reasons highlighted below.

Both power system and the customer equipment are made to function inside a range of voltages, typically inside ±5% of the nominal voltage. At low voltages, numerous kinds of equipment perform below par, induction motors can overheat and incur damage, and light bulbs deliver a reduced amount of lighting, while other electronic equipment will not function at all. High voltages can shorten equipment lifetime and damage them.

The reactive power consumes generation and transmission resources. Reactive power flow has to be minimized in order to maximize the quantity of real power that can be conveyed through a jammed transmission interface. In the same way, the production of reactive power can inhibit the power capacity of a generator.

There is significant loss of real power when moving reactive power on the transmission system. In order to compensate for these losses, both energy and capacity have to be employed.

Reactive Power and Power Factor

When the current and voltage are not in phase is when reactive power is present:

  1. Phase angle not equal to 0°
  2. One wave form leads the other
  3. Power factor less than unity
  • Power factor is measured in VAR (Volt Ampere Reactive)
  • It is produced the moment the current waveform lead the voltage form
  • It is consumed when the current waveform, lags voltage

Capacitors and Inductors

Reactors (Capacitors and inductors) are passive devices that absorb or generate reactive power. They achieve this devoid of substantial real power operating expense or losses.

Capacitor and inductor output is proportionate to the square of the voltage. Therefore, an inductor or capacitor bank that is rated at 100 MVAR absorbs or produces only 90 MVAR when the voltage drops to 0.95 Pu. However, it will absorb or produce 110 MVAR the moment voltage increases to 1.05 Pu. This association important when inductors are used in holding down voltages.

The absorption of the inductor is much higher when voltages are at the peak and the device is required most. The relationship is unsuccessful for the more common instances where the capacitors are used to sustain voltages. In extreme instances, voltages plummet, and capacitors contribute a smaller amount, causing in an additional dilapidation in voltage and even a reduced amount of sustenance from the capacitors; in the long run, voltage falls and outages come about.

Inductors are distinct devices intended to absorb a precise amount of reactive power at a precise voltage. They offer no variable control even when they are switched on or off.

Capacitor cans make up the capacitor banks. They are normally 200 kVAR or less apiece. To achieve the preferred capacitor rating and capacitor bank voltage, the cans are connected in parallel and series formations. Similar to inductors, capacitor banks are distinct devices. However, they are mostly designed with numerous steps to deliver a limited volume of variable control which makes it a drawback compared to synchronous motor.

UNDERSTANDING AND COMPARING RESISTIVE RISE AND REACTIVE BENEFIT

Resistive rise and reactive benefit are important facets that have to be considered to measure the efficiency of a given LV network. This ensures that the given LV network and the network design and layout meet the required power threshold for a given client’s need.

Both the resistive rise and reactive benefit determine the power output within a given network, the frequency and severity of voltage drops that may possibly be experienced within the network. As such, one can develop simple mathematical tools that can be used to understand and compare the level of resistive rise and reactive benefit that exist within different types of LV networks.

Note: It is important to note that the mathematical tool developed for comparing resistive and reactive benefits is the same across the different types of LV networks. When it comes to the industrial/commercial development LV network, there exist numerous uncertainties due to the nature of inadequate information on the extreme requirements based on the activities of the given customer or client. As such, certain assumptions are put in place and these uncertainties are ignored. These assumptions facilitate in the development of a simple tool as the incorporation of all these factors would lead to a very complex and exponential mathematical tool.

To develop the mathematical tool, we consider an example that involves AC voltage and current phase shift due to inductance current lags voltage as depicted in the graph below:

Time

V

ɸ

 

                                                                          I

The level resistive rise is calculated or depicted by the level of real power. From the equation above, the real power can be obtained by derived using the following equation:

Therefore, the higher the real power, the lower the resistivity rise. This calculation can be applied given different values of the parameters given, and thus can be used to compare the level of resistivity rise within a given LV network.

The reactive benefit is calculated or depicted through the value of the power factor within an LV network. The power factor is directly proportional to the value of Cos (ɸ).

REACTIVE POWER BNEFITS

Yearly min/max voltage for different cases

Comparison of voltage control methods. Base case is (a) without voltage control. In case (b) the standard PF (P) is applied and in case (C) the Q (U) is applied, with m = 4. The Q (U) control is also applied in the night, thus increasing the minimum voltage on the feeder. In case (d) the distribution transformer is upgraded to 160 kVA but without applying voltage control.

Total active power loss in transformer and cables

Energy losses for the four cases, when increasing the solar PV capacity. Minimum losses of 5.3 MWh per year are reached for a total solar PV capacity of 71 kW, but up to 107 kW can be installed and still keep the losses below the case with no solar PV.

ECONOMIC COMPARISON FOR REACTIVE POWER

Although the prospective for distributed energy based reactive supply is prodigious, currently the costs are greater than other readily available technologies, for instance capacitors. Nonetheless, not all these technologies offer the equivalent type of reactive support. Distributed energy-based reactive supply can offer active support abilities that static devices like capacitors cannot equal. Additionally, industry professionals consider that supplying reactive power from synchronized distributed energy sources can be 100% to 200% more effective than providing reactive support in bulk from extended distances at the generation or generation levels. Assessing the economics of reactive power compensation is difficult. No standard models or analysis tools exist.

Reactive power devices can be categorized as static or dynamic subject to their functionality and location. Static reactive power supply is normally found entrenched in the delivery system and provided by reactors, load tap changers on transformers and capacitors. Nonetheless, static reactive power supply cannot react to load fluctuations swiftly. This is the principal drawback of static reactive reserves and the reason the dynamic reactive reserves appeal to growing study interests.

Moreover, these kinds of devices are cumbersome in that they deliver step changes in recompense rather than an uninterrupted change. Dynamic reactive power may be delivered by devices that lie within in the following 3 classes:

  • Pure reactive power compensators for instance solid-state devices such as synchronous condensers as static compensators (STATCOM), static VAR compensators (SVC), Super VAR and D-VAR, and. They are usually classified as transmission service devices.
  • Distributed energy resources that have oversized inverters or generators in order to deliver a wider reactive power range. These DERs comprise fuel cells, diesel engine generators, micro turbines, etc. Usually, they are bought to offer backup real power (MW) supply in the case of emergency with a narrow range of reactive power production. To raise the ability of distributing reactive power, certain upgrades are essential such as oversizing the inverters for fuel cells and micro turbines and oversizing the generator for diesel engine generators. These assets are considered demand-side service or generation service depending on sizes and ownership.
  • Modifiable speed pushes to supply reactive power. Adjustable speed drives (ASD) are energy saving devices have the ability to deliver a wider range of lagging or leading lagging reactive power. ASDs can still deliver full torque short of a drop in service if they are created to transmit extra current. ASDs are also a demand-side service like customer owned DER.

Pure Reactive Power Compensators

The cost of providing reactive power comprises capital costs plus operating costs, including operating expenses and fuel costs. Capital costs of static power sources for instance capacitors, are considerably lower than the capital costs of dynamic sources for instance the D-VAR or SVC or; nevertheless, a static device will exclusively absorb or supply or absorb reactive power in fixed quantities. The cost of supplying reactive power from non-generating reactive power devices is ultimately their O&M expense and capital cost, as they do not have any fuel requirements.

Operating range in MVAR

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