Q: (i). Explain the two different techniques that can be used for condition monitoring of insulators for overhear power transmission lines.
Answer: Condition monitoring of insulators for overhead power transmission lines is critical to prevent equipment failure and service interruptions (Aggarwal, Johns, Jayasinghe and Su, 2000). Two prevalent techniques used are Visual Inspection and Non-destructive Testing.
Visual Inspection: This is the simplest, yet one of the most effective techniques for condition monitoring. In a visual inspection, trained personnel visually check the insulators for any apparent physical signs of deterioration, such as cracks, erosion, discoloration, or contamination (Farzaneh & Chisholm, 2022). This method also includes observation of insulator strings for any tilting or irregularity in alignment. Inspection can be conducted from the ground using binoculars or from close range during maintenance shutdowns. With the advent of drone technology, aerial inspections have become more common, providing a safer and more efficient means to visually inspect power lines and insulators. Drones equipped with high-resolution cameras can capture detailed images of insulators from different angles, allowing for precise evaluation of their condition.
Non-destructive Testing (NDT): This technique involves the use of advanced technologies to assess the condition of insulators without causing any damage (Zhang, et al., 2022). Several NDT methods are available, but two popular ones are:
a) Infrared Thermography: This technique uses infrared cameras to capture heat images of insulators under normal operating conditions. It’s based on the principle that an increase in temperature is often indicative of a fault. Hot spots can be indicative of increased resistive losses due to surface contamination or internal defects.
b) Ultrasonic Testing: This technique is used to detect internal defects that are not visible on the surface. Ultrasonic waves are sent into the insulator, and the reflected waves are analyzed. Any variation in the wave pattern could indicate potential flaws or defects in the insulator material.
These techniques provide utilities with an effective way of monitoring the condition of insulators and scheduling predictive maintenance, ultimately increasing the reliability and efficiency of the power transmission system. While visual inspections provide a good general overview of the insulator’s condition, NDT offers a more in-depth analysis of potential internal and non-visible external defects. The combined use of these techniques can help prevent unexpected insulator failures and reduce outage incidences.
Q: ii. BS EN 60507 (1993) provides guidance on testing high voltage insulators. Explain why the test should be carried out under wet condition?
Answer: The test for high voltage insulators, as specified in BS EN 60507 (1993), is conducted under wet conditions to simulate real-world environmental conditions that the insulators may encounter during their operational life. High voltage insulators are typically used in outdoor settings, such as power transmission and distribution systems, where they are exposed to various weather conditions, including rain, dew, and fog.
Testing under wet conditions is crucial for several reasons:
Realistic simulation: Wet conditions replicate the insulator’s exposure to moisture and surface contaminants, which can affect its performance in terms of leakage current, flashover voltage, and overall insulation resistance. Testing under wet conditions ensures that the insulator can withstand the stresses imposed by moisture and contaminants.
Performance evaluation: Wet testing allows engineers to assess the insulator’s ability to maintain its insulating properties and prevent leakage current or flashovers under moist conditions. This is essential for guaranteeing the reliable and safe operation of the equipment.
Safety assurance: Insulators must maintain their electrical integrity to ensure the safety of personnel and equipment. By testing under wet conditions, potential issues related to tracking, arcing, or electrical breakdown can be identified and addressed, reducing the risk of accidents and equipment failure.
Conducting high voltage insulator tests under wet conditions is a fundamental step in evaluating their performance and safety in real-world scenarios, ultimately contributing to the reliability and longevity of power transmission and distribution systems.
Q: (a) Calculate the ESDD Equivalent salt deposit density (mg/cm²). and the NSDD non-soluble material deposit density (mg/cm2 )
Answer: To calculate the ESDD (Equivalent Salt Deposit Density) and NSDD (Non-Soluble Material Deposit Density), we’ll use the following formulas:
ESDD (Equivalent Salt Deposit Density):
ESDD = (V * σ20) / A
NSDD (Non-Soluble Material Deposit Density):
NSDD = (Wf – 0.82) / A
V = Volume of the slurry after dissolving the deposit (in cm³)
σ20 = Volume conductivity of the slurry at 20 °C (in S/m)
A = Area of the insulator surface (in cm²)
Wf = Weight of the filter paper containing pollutants under dry conditions (in g)
Q: (b) Demonstrate your calculated ESDD and NSDD on the Figure 1 below (reproduce the Figure in your report) and determine the severity of pollution on the insulator
Answer: Given data:
Net weight of the clean filter paper (without pollutants) = 0.82 g
Weight of the filter paper containing pollutants under dry condition = Wf (g)
Area of the insulator surface (A) = 2887 cm²
Explanation of the calculations:
Step 1: Calculated the weight of the pollutants (P) on the filter paper:
P = Wf – 0.82 g
Explanation of the calculations: The Non-Soluble Material Deposit Density (NSDD) in mg/cm²:
NSDD = P / A
Now, let’s assume the value of Wf (weight of filter paper containing pollutants) is 10.5 g (for example purposes).
Step 1: The weight of the pollutants (P) on the filter paper:
P = 10.5 g – 0.82 g
P = 9.68 g
Step 2: The Non-Soluble Material Deposit Density (NSDD) in mg/cm²:
NSDD = 9.68 g / 2887 cm²
NSDD ≈ 0.003354 mg/cm² (rounded to 6 decimal places)
So, with the given values, the Non-Soluble Material Deposit Density (NSDD) is approximately 0.003354 mg/cm².
Q (c): You are going to determine the number of required insulator for a 400-kV overhead transmission line (I-string). If the leakage distance of one cap-andpin insulator is 32cm based on the recommended leaking distance per kV: determine the number of required insulators (for the location that this insulator will be installed).
Voltage level: 400 kV
Leakage distance per kV based on Table 1:
Very Light: 1.5 cm/kV
Light: 1.6 cm/kV
Moderate (Medium): 2.0 cm/kV
Heavy: 2.5 cm/kV
Very Heavy: 3.1 cm/kV
Analysis: The total leakage distance required for 400 kV:
Total Leakage Distance (cm) = Voltage (kV) * Leakage Distance per kV (cm/kV)
Using the Moderate (Medium) leakage distance (2.0 cm/kV) as it is a common and safe choice:
Total Leakage Distance = 400 kV * 2.0 cm/kV Total Leakage Distance = 800 cm
Now let us determine the number of required insulators:
Number of Insulators = Total Leakage Distance / Leakage Distance of one Insulator Number of Insulators = 800 cm / 32 cm/insulator Number of Insulators = 25 insulators
So, for the location where this insulator will be installed, it will need 25 cap-and-pin insulators for the 400-kV overhead transmission line, assuming a leakage distance of 32 cm per insulator and using the moderate (medium) value.
Aggarwal, R.K., Johns, A.T., Jayasinghe, J.A.S.B. and Su, W., 2000. An overview of the condition monitoring of overhead lines. Electric Power systems research, 53(1), pp.15-22.
Farzaneh, M. and Chisholm, W.A., 2022. Protective Coatings for Overhead Lines in Winter Conditions. In Techniques for Protecting Overhead Lines in Winter Conditions: Dimensioning, Icephobic Surfaces, De-Icing Strategies (pp. 195-309). Cham: Springer International Publishing.
Zhang, X., Cheng, L., Liu, Y., Tao, B., Wang, J. and Liao, R., 2022. A review of non-destructive methods for the detection tiny defects within organic insulating materials. Frontiers in Materials, 9, p.995516.