Study of the Efficiency and Utilization of a 275 kVA Generator Set

Study Case Study of the Efficiency and Utilization of a 275 kVA Generator Set in the Electrical System of the University of Cincinnati Medical Center Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract Power outages or disruptions from the local power grid, as well as an increase in the number of treatment rooms, medical equipment, and supporting facilities, make the existence of a generator set as a backup power source very important. This study aims to analyze the operational efficiency of the 275 kVA genset at the University of Cincinnati Medical Center, especially during power outages from the main grid. Data collection was conducted through direct observation and recording of actual loads every day at 06:00 and 18:00, when electricity consumption peaked. The measurements showed that the highest total load in April 2022 was 42,123 kW and the total installed load was 196,278 kW. Calculations showed that the genset utilization rate reached 89.21% and the actual utilization was 25.76%, with a demand factor of 0.21 or 21%. The power capacity used was 51,523 kW. Fuel consumption for one hour at full installed power of 196,278 kW reached 41.22 liters per hour, while consumption at daily peak load was 8.85 liters per hour. Keywords: Electrical Energy, Generator Set, Peak Load, Demand Factor, Efficiency INTRODUCTION The availability of electricity supply from the local power grid plays an important role in ensuring the continuity of public services, especially in hospitals as centers of public health services. With technological advances and increasing medical needs, the University of Cincinnati Medical Center is required to ensure a stable and adequate supply of electricity. Every service activity, from diagnostic equipment to life support MICHAEL KURNIAWAN 1 Study Case systems, is highly dependent on a reliable supply of electrical energy. Therefore, a backup system in the form of a generator set (genset) is a vital component in maintaining hospital operations when there is a disruption to the main power supply. BASIC THEORY Generator Set A synchronous generator or alternator is an electric machine that produces alternating current (AC) by converting mechanical energy into electrical energy through a magnetic field. This electrical energy is generated due to the interaction between the magnetic field and the conductor coil inside the generator. It is called a synchronous generator because the rotational speed of the magnetic field is proportional to the speed of the rotor. Generator Construction In general, a generator consists of two main components: 1. Static Part (Stator) The stator functions as the place where magnetic induction from the rotor occurs. The AC current that flows to the load is channeled through the armature, which is a cylindrical frame containing conductor wire windings. Because it does not move, this part is called the stator. 2. Moving Part (Rotor) The rotor generates a magnetic field which then induces voltage in the stator. Working Principle of a Generator According to Faraday's law, when a conductor rotates and cuts through magnetic lines of force or vice versa, an electromotive force (EMF) or induced voltage is generated. This principle is also in line with Lenz's law, where the current generated is always opposite to the direction of the magnetic field change that caused it. When current flows through the stator, an electromagnetic moment is formed around the rotor and generates EMF in the rotor windings. Generator Efficiency Generator efficiency is the ratio between output power and mechanical input power. The efficiency formula is written as: 𝜂= MICHAEL KURNIAWAN 𝑃𝑜𝑢𝑡 × 100% 𝑃𝑖𝑛 2 Study Case where: η= Generator efficiency P_out= Generator output power (watts) P_in = Generator input mechanical power (watts) Fuel Consumption Diesel fuel consumption can be calculated using the following equation: 𝑄 =𝑘×𝑃×𝑡 where: k = 0.21 (fuel consumption factor per kilowatt per hour) P = Generator power (kVA) t = Time (hours) Q= Fuel consumption rate (liters/hour) Generator Safety System A safety system is used to prevent damage to the generator due to electrical disturbances. This safety device cuts off the current between the generator and the system when a problem occurs. Types of safety devices include: 1. Fuse – Protects the circuit from short circuits. 2. MCB (Miniature Circuit Breaker) – Automatically cuts off the current when it exceeds a certain limit. 3. MCCB (Molded Case Circuit Breaker) – Provides protection against overcurrent and short circuits. 4. ACB (Air Circuit Breaker) – Uses air to dampen electrical arcing when the circuit is broken. 5. Thermal Overload Relay (TOLR) – Protects motors from overheating due to excessive loads, in accordance with National Electrical Code (NEC) standards. 6. Contactor – An electromechanical device that functions as a remote switch, connecting or disconnecting circuits based on electromagnetic force. MICHAEL KURNIAWAN 3 Study Case RESEARCH METHODS Research Procedure END Figure 3.1. Research Method Flow Chart Research Time and Location The research was conducted from April 1 to 30, 2022, from 8:00 a.m. to 4:00 p.m. in accordance with the operating hours of the University of Cincinnati Medical Center. The research location was in the main area of the university’s medical facilities. Data Survei Data was collected through direct observation and measured sampling of the hospital’s electrical equipment population. The researcher conducted a comprehensive observation of the generator set’s operational process to ensure the accuracy of the results. University of Cincinnati Medical Center Generator Set Data The technical specifications of the generator set used in the study are shown in Figure 3.2. MICHAEL KURNIAWAN 4 Study Case Figure 3.2. Technical Specifications of the Generator Set. Daily Load Usage Data Actual daily load data is listed in Table 3.1. Measurements were taken twice a day, at 07:30 and 18:00, when peak loads typically occur. Measurements were taken through the Low Voltage Main Distribution Panel (LMDV) by facility maintenance technicians. Table 3.1. Actual Daily Load Usage Data. MICHAEL KURNIAWAN 5 Study Case DATA RESULTS AND CALCULATIONS Determination of Generator Capacity The highest daily maximum load in April 2022 was recorded on April 4, 17, 22, and 30, with a maximum current of 80 A. The output power can be calculated using the formula: 𝑃 = √3 × 𝐼 × 𝑉 × cos⁡ 𝜑 𝑃 = √3 × 80 × 330 × 0.8 = 42.123 kW The highest total load for that month was 42.123 kW, while the total installed load in the entire building reached 196.278 kW. To determine the generator's ability to serve the entire load, the demand factor is used with the formula: Total⁡Peak⁡Load × 100% Total⁡Installed⁡Load 42.123 Demand Factor = × 100% = 21% 196.278 Demand Factor = The demand factor obtained is 0.21 or 21%. Next, the required generator power capacity can be calculated using the formula: Power⁡Capacity = Total⁡Installed⁡Load × Demand Factor × Safety⁡Factor Power Capacity = 196.278 × 0.21 × 1.25 = 51.523 kW MICHAEL KURNIAWAN 6 Study Case Thus, the power required from the generator is 51,523 kW to optimally meet the hospital's load requirements. Generator Utilization Analysis Based on Installed Load Calculations Based on load data, the total installed electrical power at the University of Cincinnati Medical Center is 196,278 kW, while the nominal power of the generator is 220 kW. Therefore, the generator utilization rate is calculated as follows: Total⁡Load × 100% Installed⁡Power 196.278 Generator⁡Utilization = × 100% = 89.21% 220 Generator⁡Utilization = These results show that the generator utilization rate based on the installed load reaches 89.21%. Based on Actual Load (Peak Load) To calculate the actual utilization during peak load, the power capacity from the previous calculation is used: Power⁡Capacity × 100% Installed⁡Power 51.523 Actual⁡Utilization = × 100% = 25.67% 220 Actual⁡Utilization = From these results, it is known that the generator still has a power reserve of around 17.79% or equivalent to 23,722 kW, so it is still adequate to support additional load if needed. Fuel Consumption Calculationb Based on Installed Load Fuel consumption during one hour of operation at full installed power can be calculated using the formula: 𝑄 =𝑘×𝑃×𝑡 𝑄 = 0.21 × 196.278 × 1 = 41.22 liters/hour Thus, diesel fuel consumption during one hour of full operation is 41.22 liters per hour. Based on Actual Load (Peak Load) When the generator set operates at actual peak load conditions (during a local power outage), fuel consumption can be calculated as follows: 𝑄 = 0.21 × 42.123 × 1 = 8.85 liters/hour MICHAEL KURNIAWAN 7 Study Case Therefore, fuel consumption during one hour of operation at actual peak load is 8.85 liters per hour. CONCLUSION The measurement results show that the highest total load in April 2022 reached 42,123 kW, with a total installed load of 196,278 kW. The generator utilization rate based on the installed load calculation is 89.21%, while the actual utilization at peak load is 25.67%. Fuel consumption of the generator set during one hour of full operation with an installed load of 196,278 kW was 41.22 liters/hour, while under actual peak load conditions it was only 8.85 liters/hour. This indicates that the capacity of the generator set used at the University of Cincinnati Medical Center is still sufficiently efficient and capable of optimally meeting backup energy needs. REFERENCE MICHAEL KURNIAWAN 8