Contents 1.1 Objectives: ..................................................................................................................................................3 1.2 Introduction: ..............................................................................................................................................3 1.3 Experimental Setup: ..................................................................................................................................4 1.4 Procedure: ..................................................................................................................................................4 1.5 Results:........................................................................................................................................................6 1.6 Discussions: ................................................................................................................................................8 1.7 Conclusions: ...............................................................................................................................................8 EXPERIMENT NO 2: REAL TIME VERIFICATION OF CIRCUIT BREAKER TIME-CURRENT CHARACTERISTICS 1.1 Objectives: In this lab, we will learn to: To become familiar with power circuit breakers To observe time-current characteristics of circuit breaker 1.2 Introduction: Time-current curves are graphical representations of the trip characteristics of a circuit breaker. These curves show the relationship between the magnitude of the current flowing through the circuit breaker and the time it takes for the circuit breaker to trip. This information is critical for ensuring that the circuit breaker provides adequate protection for the equipment it is connected to. Time-current curves are typically provided by the manufacturer of the circuit breaker and are based on industry standards such as the Institute of Electrical and Electronics Engineers (IEEE) and the National Electrical Manufacturers Association (NEMA). Figure 1Trip characteristics of circuit breaker The time-current characteristic of a circuit-breaker sets the tripping time depending on the value of the overcurrent flowing in its main circuit. The time-current characteristic of each circuit-breaker must, on the one hand, predetermine its reliable protection of the conductors of electrical circuits against overcurrent. The circuit-breaker must shut down the circuits in time to prevent the conductors from overheating.On the other hand, it must prevent the tripping of the circuit-breaker when an electric current equal to the rated current is flowing in its main circuit, provided that the ambient temperature does not exceed a reference ambient temperature of 30° C.In addition, the timecurrent characteristics of the circuit-breaker must be such that it is possible to avoid tripping the inrush currents flowing in the circuit when the electrical equipment is switched on. Figure 2Circuit Breaker 1.3 Experimental Setup: Figure 3Experimental Setup to determine trip characteristics 1.4 Procedure In the first experiment we will simulate a blocked pump. The pump should initially run to nominal load. An object in the water causes the pump to be blocked suddenly. This causes an increase in output power of motor (P = Tw) because a sudden blockage causes a requirement of high output power to put more pressure on it. Since the load has increased, torque increases, the first impact is of decreasing speed but it is possible up to a certain extent. After that, armature current increases (increasing the input power to the motor). So, a higher current flow through the motor as a result of this blockage. After several second the motor should be switched off by the circuit breaker. In order to be able to simulate this fault proceed as follows: • Start the ActiveServo software. Switch to the menu 'Timing diagram'. • Open the window to set the torque characteristic and set the following torque characteristic: The motor should run up to nominal operation with the first 20 seconds (approx. 2.2 Nm). After 20s an object gets caught in the pump causing a blockage (set to approx. 8Nm). Set a measurement time of 100s and activate the rms measurement. Start the brake. Switch the servo machine test stand to 'RUN'. Start the recording of the characteristic. Switch the circuit breaker on. • • • • The motor should now run at no-load speed while the characteristics are recorded. After approx. 20 s copy the torque characteristic to the test stand. Copy the characteristic into the following diagram: Now in the second scenario, we will consider a load with high inertia and see its effect as well. We consider a flywheel load from ActiveServo Software. Switch the load to flywheel under the Settings --> Loading machine. • • • • • • Select a flywheel mass of 800 in the parameters and a friction level of 35. Change the measurement time to 100s and choose the option RMS. Change the display of the measured values and the diagram distribution as required. Start the brake. Switch the servo machine test stand to 'RUN'. Start recording the characteristic. 1.5 Results: Figure 4\Response of motor to time independant load Figure 5Response of motor to flywheel : Figure 6Time chracteristic curve of motor Figure 7Response of motor to pump 1.5.1 About Results : The delay in the trip of a circuit breaker when a flywheel is connected as a load is primarily due to the kinetic energy stored in the flywheel. When a flywheel is spinning at a high speed, it has significant rotational kinetic energy, and this energy needs to be dissipated or brought to a stop when the circuit breaker is tripped. Flywheels are designed to have high inertia, which means they resist changes in their rotational motion. This inertia results from the mass of the flywheel and its distance from the center of rotation (moment of inertia). When the circuit breaker is tripped, it takes time for the flywheel to decelerate and stop due to its inertia.: The energy stored in the flywheel needs to be transferred elsewhere, typically converted to other forms of energy (e.g., heat through braking systems or electrical resistance). This process takes time, as the energy transfer rate is not instant. Brake Systems: Many flywheel systems are equipped with braking mechanisms to slow down and stop the flywheel when needed. These brake systems themselves have a delay in their activation and effectiveness.: The control system that triggers the circuit breaker and associated safety mechanisms may also introduce a delay in responding to a fault or overload condition. It's crucial to ensure that the control systems are designed to coordinate the operation of the circuit breaker with the slowing down or stopping of the flywheel 1.6 Discussions: The experiment aimed to assess the real-time performance of circuit breakers under various load conditions. The time-current characteristics were measured in real-time, and the data were recorded as per the outlined procedures. Data collection proceeded smoothly without any significant issues. The obtained time-current characteristics were compared to industry standards. Our results showed that the circuit breakers closely matched the manufacturer's specifications, with minor variations within the acceptable tolerance. Under various load conditions, the circuit breakers performed as expected, tripping within the defined time frame. The breakers demonstrated robust performance from normal operation to fault conditions. Sensitivity and accuracy testing indicated consistent performance across multiple trials and different circuit breakers, supporting the reliability of the devices. Environmental factors, such as temperature and humidity, did not have a significant impact on the circuit breaker's performance. The breakers exhibited consistent behavior across a range of conditions.The circuit breakers demonstrated no notable operational limitations in our testing. They effectively handled various types of faults and overloads within their specified ratings. 1.7 Conclusions: In summary, this experiment provided valuable insights into the real-time verification of circuit breaker time-current characteristics. The circuit breakers tested in this study exhibited reliable and consistent performance in accordance with their time-current characteristics. They effectively protected electrical systems from overloads and faults The circuit breakers complied with both manufacturer specifications and relevant industry standards, underscoring their reliability and adherence to safety protocols The results of this study confirm the circuit breakers' reliability and safety in ensuring the protection of electrical systems and preventing damage or injury. Future research could explore the long-term performance of circuit breakers in real-world applications and their ability to withstand a wider range of environmental conditionsThis study is significant as it reinforces the confidence in the circuit breakers' ability to protect electrical systems and ensures their continued safe and reliable operation.This experiment had certain limitations, such as the focus on a specific set of circuit breakers and idealized laboratory conditions. Further studies may consider a broader range of circuit breaker types 1.8 References: 1. https://ieeexplore.ieee.org/book/5264125 2. https://link.springer.com/book/10.1007/978-1-4615-3072-5
