Line Losses, Voltage Drop and Voltage Unbalance on Parallel Overhead Distribution Lines

Abstract

It has been a general practice by distribution utilities to parallel overhead distribution lines/feeders in a common right of way and the same pole as they terminate from a common substation. This paper studies the impact of modeling parallel overhead distribution lines. The modeling of this kind of circuits in the regulated status of electric distribution business is important as the modeling can impact line losses, voltage drop and voltage unbalance in the lines. A sample case was set-up and is simulated in two cases; parallel lines modeling and taking the parallel lines individually. The study utilized load flow calculations for analyzing line losses, voltage drops and voltage unbalance. The results showed that line losses are not affected by the kind of modeling applied to parallel overhead distribution lines but voltage drop and voltage unbalance yielded different results in the two cases simulated.

See full paper - Parallel Distribution Lines

Philippine Electric Cooperative Analysis : Circuit Kilometer and Number of Customers

The figure on the right is a graphic illustration of Philippine Electric Cooperative Data for their circuit kilometer of their distribution power lines and number of interconnected customers in their electric systems.

From the figure, Electric Cooperative (EC) number 2 has the lowest number of customers while EC #86 has the most number of customers being served. For the circuit kilometer (CKM), EC #91 has the longest distribution lines while EC #33 operates the shortest CKM.

It is interesting to note that EC #91 has the longest CKM and yet serve a number of customers which is less than the number of customers of EC #86. The area franchise of EC #91 maybe very large and rural that it takes to build, operate and maintain such length of distribution lines with such medium number of electric consumers. EC #86 has the highest number of customers and yet operate a not so longer distribution circuits. It can be hypothesized that the area served by EC #86 is very electric power dense. Same evaluation can be derived with EC numbers 2 and 33.

In this case, regulatory considerations for project investing for Philippine electric cooperatives must consider how the service area of an EC is electrically dense or not. If the analysis above does not stand with the density of the franchise, then EC #91 has over built distribution lines while EC #86 can be said to have efficiently invested in electric power distribution lines for a greater number of customers.

Static Voltage Stability Analysis for Electric Subtransmission Systems

The study of voltage stability as indicated in the Philippine Grid Code (PGC) is the center of this paper. Standards and industry practice for voltage stability problem-solving are cited and were referred when provided an example simulation. Voltage stability is a must when looking at a power system if it can handle load growth and at the same time maintaining acceptable voltage levels at all system nodes pre and post-contingency. The static voltage stability simulations utilized practical solutions for voltage instability which are discussed and evaluated using Power-Voltage (PV) and Voltage-MVAR (VQ) curves. This report serves as a tutorial for practicing engineers on the important topic of voltage stability.

See paper by clicking this - Static Voltage Stability Analysis for Electric Subtransmission Systems

Philippine Electric Cooperative Data

It is interesting to study the electric cooperatives’ data publicly posted in websites. The following websites provides these data:

• Energy Regulatory Commission (ERC)
• National Electrification Administration (NEA)

Primarily, the ERC data has the following columns:

1. Distribution line length in circuit-kilometers (ckm) – this item refers to the existing overhead lines owned by each electric cooperative. The data must include single-phase, two-phase and three-phase distribution circuits operated in the cooperative’s franchise area, irregardless of voltage level.

2. Number of customers – the total sum of all electric consumers in each electric cooperative service area. This may be the total of residential plus commercial plus industrial plus barangay electrification. Normally this data is the number of electric meters being maintained by the cooperative.

3. Sales volume – this data is in MWh unit. The total sales of each electric cooperative in year 2006 which was supplied to the total number of customers and which was procured from the transmission operator or other electric power supply entities.

4. Consumption per customer – this data is obtained from dividing data number 3 to data number 4. Though looking at average, this is an indicator of how much energy is utilized by each facility.

5. Structure – is the ratio of the mix of residential sales plus barangay electrification to the total energy sales. This shows on how “rural” is the service area of the electric cooperative. A higher value of structure tells us that that the service area is that the demand comprises much of residential and barangay electrification which is more rural, while a lower structure value gives an indication that the service area has commercial and industrial bulk of energy users.

6. Density - this data is MWh sales divided by the ckm of distribution lines. This reveals how much dense is the service area of the electric cooperative in terms of loading in distribution lines.

7. Distribution Supply Metering (DSM) charge – this data is presented in peso per kwh is reflected in the electric bill.

NEA has many available data but in this article we will focus only on two:

1. Reliability score – ERC has promulgated reliability guidelines for electric distribution companies using standard indices. Reliability is the capability of the electric cooperative to minimize frequency and duration of unforced outage in their service area. In this data, NEA may have summarized the electric cooperative data into one single score.
2. Power Quality (PQ) score – same with reliability, PQ is a performance indicator for electric distribution companies, but in this case ERC has devised their own indices. Also, NEA may have summarized the electric cooperative data into one PQ single score.

In the coming articles, I will try to analyze these data and extract technical and objective evaluation thereof.

SEARCHING FOR THE NEW ERC CHIEF

Reactions from the senators on the likely to be appointed new ERC Chief, see this link - http://www.journal.com.ph/index.php?issue=2008-07-10&sec=4&aid=66133

The senators talked sense!!!

Winning TransCo bidder to get franchise soon

A Philippine congressman giving some false lessons in power systems, see this link:

Winning TransCo bidder to get franchise soon

News Impacting Electricity Rates

Napocor seeks ERC clarification on rate cut

Power subsidy sought from Malampaya proceeds

PSALM opens bidding for Iligan power plant

WESM power rates drop to all-time low

MANILA, Philippines – Despite increasing fuel costs, electricity rates at the Wholesale Electricity Spot Market (WESM) dropped at an all-time low, QTV’s Balitanghali reported Tuesday.

According to the report, power rates at WESM dropped to P1.80 per kilowatthour (kWh), around P2 lower than its rates in previous months when the rates were around P4 to P5.

The report quoted Lasse Holopainen, president of the Philippine Electric Market Corporation (PEMC), as saying that the power cut would lower the generation charge incurred by distributors like the Manila Electric Co. (Meralco).

In fact, this decline in WESM's power rates translate to a 30 to 40-centavo per kWh reduction in Meralco's electricity rates.

Holopainen said that the power rates at the WESM plummeted due to the recent drop in temperature in the country. He said that a colder weather prompts power consumers to use less electricity, thereby lowering the demand for power.

The PEMC president also said that the productivity of hydro-electric power plants shot up due to the occasional rain showers and series of typhoons that visited the country.

Aside from the generation charge, a consumer’s electricity bill is also dependent on other factors like system loss. The Meralco had earlier said that it has also incurred a lower system loss in June, which is also set to slash power rates further.

Meralco Vice President Elpi Cuna has said that the Meralco’s system loss charges will go down by as much as six centavos per kWh. - Mark Merueñas, GMANews.TV

Fuzzy Optimization for Distributed Generation Allocation

Abstract— Distributed generation (DG) allocation problem is addressed utilizing fuzzy multi-objective optimization in this paper. It is shown that the methodology provides needed consideration for DG allocation and accounts for uncertainty using fuzzy set theory. Voltage drop reduction, short circuit capacity (SCC) augmentation, decrease operation cost and system losses reduction were considered as objectives for formulating fuzzy optimization. The paper discusses in detail the approach adopted and several numerical examples are presented to test the developed methodology.

Full paper -Fuzzy Optimization For Distributed Generation Allocation

Integrating Power Quality in Power System Planning

Power Quality (PQ) has become a major concern in electric power systems with the increased proliferation of computer electronic loads and power electronic devices in the power system, and more consumer interest in power delivery issues. Understanding PQ requires taking on the viewpoints of the electric utilities, consumers and operators of electrical equipment. Regulatory codes require compliance with stated standards of power system performance measured in terms of quality and reliability. Yet notwithstanding all the quantitative and qualitative technical aspects of PQ, it has heretofore remained primarily a consequential characteristic rather than a planned objective for power systems. Perhaps it is time to consider integrating PQ objectives in the planning process. As such, PQ must fit in with all the other objectives of power system planning – thermal capacity adequacy, voltage security, stability, etc. The challenge for the planner is to take into account the already complicated planning process and integrate PQ.

Different conventional planning tools are utilized for power system planning: power flow studies, short circuit calculations, transient stability analysis and electromagnetic transient simulations, among others. The different planning time horizons utilized in these tools can be utilized for analyzing PQ issues arising from the simulations since PQ concerns account for time ranges.

Case studies show how PQ concepts can be applied to power system planning. Overall, there are opportunities to integrate PQ analysis in conventional power system planning studies. The above discussion of integrating PQ analysis in various studies can be useful in providing a PQ viewpoint in the planning of electric power systems. The result is a power system planned and operated not only for economics and reliability but also for power quality.

Please see the complete article - http://www.pterra.com/Pterra%20Tech%20Blog%2026%20-%20PQ%20Planning.pdf

Harmonic Penetration in Electric Transmission Systems

When the physicians of the power system (planners and operators) treat for resource inadequacy, congestion, instability and all the modern-day maladies of competitive power markets, their regimen may come with an increasingly common side effect – harmonics. The utilization of static var compensators (SVC), induction generators, source converters, underground and submarine cables, direct current converters, to name a few, to provide solutions to power system problems can lead to increasing harmonic penetration in the power system. Harmonic generating equipment coupled with system resonance conditions effects are cumulative and can be detrimental to system operations if not mitigated.

See the complete article on this link - http://www.pterra.com/Pterra%20Tech%20Blog%2024%20-%20Harmonics.pdf

Concept for Distribution System Planning

Rationale - Since distribution utilities (DUs) are regulated with their operational power quality (PQ) and system reliability, which accounts for System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI), it may be considered to utilize the historical data for DU planning in the context of probabilistic evaluation.

Concept Methodology-

1. Gather PQ and DU system reliability data for a certain time range, maybe five years.
2. Establish level of PQ, SAIFI and SAIDI to be utilized for planning purposes by applying 95% probability acceptance.
2. Identify planning alternatives to solve problems of PQ and system reliability.
3. Compute and simulate levels of PQ, SAIFI and SAIDI per planning alternative.
3.1. This may utilize DU system reliability software/spreadsheet and PQ program simulation.
4. Compute relative system unreliability cost and cost incurred for poor PQ for each planning alternative.
4.1. System Unreliability Cost = SAIDI x Cost of electricity (P/kWH)
4.2. Poor PQ Cost = Energy Losses (due to Poor PQ) x Cost of electricity (P/kWH)
5. Compute total cost of each alternative.
5.1. Total Cost = Invesment Cost + Operational Cost + System Unreliability Cost + Poor PQ Cost
6. Two Methods for Planning Altenratives Comparison
6.1. Compare Total Costs of Planning Alternatives.
6.2. Benefit/Cost (B/C) Method, where [(Base Reliability + Base PQ) - (Alternative Reliability + Alternative PQ)]/ Total Cost of Alternative
7. Choosing appropriate planning alternative.
7.1. Choose planning alternative with Lowest Total Cost.
7.2. Choose planning alternative with Highest B/C.

Computer Tools in Power Systems Courses in the Philippines

At the deregulation of electric power industry, technical and value-based studies for planning and operations of power systems as outlined in electricity regulatory codes should be integrated in electrical engineering programs and promote the present scenario by undertaking power systems applications and incorporate computer simulations to stimulate students’ interest and increase their insights with the on-going deregulation of the industry.

The restructuring of the Philippine electricity industry gives a new facet not only to the industry itself but to the education and training of the present and future electrical engineers. With codes and economics governing the operation of electric power systems in the country, challenges in academic instruction to prepare students get ready for work after graduation or board exams remains a daunting task. Technical and value-based planning and operations of these power systems as outlined in should be integrated in the electrical engineering curriculum and elevate the present scenario by undertaking power systems applications and incorporate computer simulations to stimulate students’ interest and increase their insights with the on-going deregulation of the industry. Further, many power system analysis applications that are straightforwardly undertaken using computer programs are required for operations, planning and interconnections.

Recent regulatory filings included the utilization of power system simulations thru suggested software or computer programs. Given this, power industry restructuring education must be started as early as possible to equipped young engineers-to-be by integrating computer simulations into power systems courses taught in the universities. Moreover, the electrical engineering faculty must also take serious measures to keep in-step of the industry changes and challenges in order to prepare students in practical applications by using computer tools.

Acquiring power system software nowadays is not a difficulty experienced in introducing computer simulations in power system courses since some commercial type programs are free with student or demo versions provided for educational and research purposes or even incorporated in power system textbooks. It should be noted that these educational versions are for use only as teaching and research tools and not for commercial purposes. Experiences of classroom utilization of power system simulations are not new and were practically appreciated. It is not the purpose of computer simulations to replace manual computations but to enhance and nourish student learning insights.

Recognizing to resolve the issues discussed above, the integration of the use of computer tools, specifically, PowerWorld, PSCAD/EMTDC and Radial Distribution Analysis Program (RDAP) in power system courses at undergraduate and graduate electrical engineering programs at Holy Angel University (HAU) in Angeles City, Philippines is recently conducted. PowerWorld (http://www.powerworld.com/DemoSoftware/GloverSarmaSimdwnldv13.asp) software is utilized for bulk transmission system planning and operations specifically power flow, short circuit, economic dispatch and contingency analysis. PSCAD/EMTDC (http://pscad.com/download-download.php) is an electromagnetic transients program but was used for power system control lectures while Radial Distribution Analysis Program (RDAP) (http://www.zianet.com/whpower/whpc3.html) is a three phase load flow and short circuit DOS program utilized for electric power distribution systems lectures and projects. The utilization of these power system computer programs is incidental since student or educational versions are provided for free thus it is not the aim to endorse the said specific power system softwares.

Analysis of the Visayas Power Situation

Recent newspaper reports indicated that the Department of Energy (DOE) has deferred the launching of the commercial operations of Wholesale Electricity Spot Market (WESM) in the Visayas region due to the report of an Australian firm, Intelligent Energy Systems (IES) (http://www.philstar.com/archives.php?aid=200804157&type=2&). IES was commissioned by DOE to assess the readiness of the said region in having an electricity market operation.

IES reports the following:

• Visayas region is not ready to have its own electricity market due to the inadequacy of power supply.
• Upgrading of transmission lines as one of the remedial measures to prevent any power shortages or interruptions.
• Market participants must have long-term contracts for their power supply.
• The estimated peak demand for Visayas is 1300MW while the available generation capacity is 1700MW plus the High Voltage Direct Current (HVDC) link output of 150MW.
• Visayas is suffering from scarce of generation reserves.
• Involuntary load shedding or manual interruption of power is practiced regularly in the Visayas grid.

Here are my thoughts based on the newspapers’ and news websites’ reports:

1. Inadequacy of generation is one main reason why an electricity market should not be established. DOE knows this even beforehand since they report power statistics in their website (http://www.doe.gov.ph/EP/Powerstat.htm). Electricity market brings competition to the generation sector thus with scarce of power supply this will not be true further.
2. Upgrading of existing transmission lines to prevent power shortages may fall short to solve the problem. Imagine having a two bus system with a transmission line of good capacity where the amount of load is almost equal to the generation. Here’s the scenario, if some of the generation may be out for maintenance or some plant trouble, then reserves is not sufficient and may impact the reliability and quality of supply at the loads. If we add another transmission line this will increase the transfer capability of generation to the load but will not increase the amount of generation and reserves since the system is out of power generation! Though generation competition requires transmission capacity, this does not solve generation scarcity in the Visayas grid.
3. Long term contracts will freeze the electricity price whether in a market situation or regulated conditions. This is a good approach for hedging in markets.
4. The evaluation of the real power generation (MW) is a welcome approach but may not be complete since reactive power (MVAR) should be integrated. Visayas grid suffers from voltage problems with generation deficit plus insufficient MVAR sources. Note that the 1700MW generation can help to provide MVARs but having mostly 69kV systems, in case of Visayas, this reactive power may be not enough.
5. Reserves are needed for operating a power system. These are resources that can be relied upon in the event the power system experiences untoward disturbance. In an electricity market, these resources are allocated and paid accordingly. Having insufficient reserves will fail the spirit of competition in an electricity market.
6. Load shedding or dropping may be cause by underfrequency or undervoltage. This is a result of under generation. Payment to the dropped loads must be given since they help out in alleviating operational constraints in the Visayas grid. Loads that are shed are acting as “reserves” in this case, so incentives must be attributed to them.

Overall, to solve the Visayas power situation, the regulation and politics of power generation investment in the Philippines must be set aside. Generation sector is a competitive business; the energy regulator must keep itself from a distance with the power generation business. Cross-ownership in the power sector must be seriously looked into since this will impact incoming generation investments. The government must show its integrity and strong support to generation investments and keep its hands clean toward unwanted corruption in the electric power industry.

Voltage Security in Philippine Power Systems

Voltage security in power system planning and operations is an important factor of grid and distribution codes in the Philippines. The power system, system components and customer devices respond to the magnitude of voltage in a manner that would impact its operation. Power system interruption cascades when voltage collapse is experienced. Generators and other system elements tend to be saturated when keeping the voltage secured at certain limits. Customer devices might misoperate or may expel from its connection point when voltage is not appropriately within the devices’ operating regions. These are some of the reasons why it is important for a power system to be planned and operated in terms of voltage security. With areas where generation deficit is a problem, voltage security is hard to achieve since generators provide and assist in keeping the voltage secured in terms of reactive power management.

Philippine transmission systems must be operated in normal conditions within voltages of 0.95 per-unit up to 1.05 per-unit while distribution systems are expected to have voltage levels from 0.90 per-unit to 1.10 per-unit. These voltage magnitudes should be kept in steady-state conditions. Scheduled maintenance of lines and other components must be conducted making sure that these voltage performance standards must be kept. When a fault or a transient event occurs, the voltage levels can not deviate from 0.90 per-unit to 1.10 per-unit as long as 0.00833 seconds to 60 seconds. In this case, voltages magnitudes are classified as voltage sags or swells. Above 60 seconds, and the voltage levels are still deviating from the said limitations, these voltages are called long duration voltage variations.

Voltage security can be planned and operated by reactive power management and predicting the voltage profile in contingency analysis. Reactive power supervision entails updated reactive power capability curves of existing generators and list of static and dynamic reactive power devices installed in the power systems. When running a post-contingency voltage assessment, the reactive power capabilities of generators, reactors, capacitors and static VAR devices (SVDs), and operating points of tap-changing transformers, must be considered since these options can be enable in running appropriate post-contingency power flow solution. The area/zone/buses in study must be identified by the power system engineer(s) for proper scenario and conditions setting. The voltage ranges limits and voltage deviation limits must be defined for the area or zone or buses in study for analysis purposes. Together with the identification of the area in study, possible system contingency scenarios, assigning of voltage limits at the area in study the power flow solution or transient simulation can be automatically configured to report all the violations as a result of each probable contingency. Usually, in power flow computations, these can be presented in tables or graphs while for transient simulations, whether in phase domain or time domain, these voltages are analyzed using time versus voltage plots.

Philippine power systems just like any other power systems must be operated in voltage security. Voltage must be operated and planned accordingly for the power system and its components to operate securely. Codes define limitations and thus appropriate prediction and prevention of unsecured voltage can be analyzed. Knowledge of existing reactive power devices in the power system and proper coordination of these devices will enhance voltage security together with applying computer solutions that can automatically provide flexible programming of studying areas of voltage violations.