General Aspects of a Good Distribution System
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. What are the requirements of a good distributed system ?
Advantages - Disadvantages
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. Write a note on various d.c. systems.
Three Phase Three Wire System - Three Phase Four Wire System - Advantages - Disadvantages
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. Explain the various types of a.c. systems.
Transmission and Distribution
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Now a days, an electrical energy is generated, transmitted and distributed in the alternating form. This is because of the fact that the alternating voltages can be raised or lowered in magnitudes by the use of transformers.
Transmission and Distribution
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Transmission and Distribution: Unit V: Distribution Systems : Syllabus, Contents
Transmission and Distribution | Underground Cables
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Transmission and Distribution: Unit IV: Underground Cables : Two Marks Questions with Answers
Underground Cables
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Question : 1. Write a note on thermal rating of cables.
Thermal Characteristics Thermal Resistance of Single Core Cable - Thermal Resistance of Soil
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Questions : 1. Explain the thermal characteristics of a cable. 2. Write a note on heat flow in a cable.
Copper Loss - Dielectric Loss - Sheath Loss
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Question : 1. Explain the various losses in a cable responsible for producing heat.
Measurement of CS and CC
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Questions : 1. Describe an experiment to determine the capacitance of a belted 3 phase cable. 2. Derive an expression for the capacitance of a three core cable and the charging current. 3. A3 core, 3 phase metal sheathed cable gave the following results on testing for cables : i) Capacitance between all conductors bunched and the sheath is 0.9 µF. ii) Capacitance between two conductors bunched connected to sheath and third conductor is 0.4 µF. Calculate, a) Capacitance between any two conductors b) The capacitance to neutral c) The charging current taken by the cable when connected to 22 kV, 3 phase, 50 Hz system.
Use of Intersheaths - Capacitance - Difficulties
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables
Questions : 1. What is grading of cables ? Discuss the capacitance grading of cables in detail. 2. Discuss the intersheath grading of cables in detail. 3. With neat diagram, explain the various methods of grading of underground cables. 4. A single core lead sheathed cable is graded using two dielectrics of relative permittivity 3.6 (inner) and 2.5(outer), the thickness of each being 1 cm. The core diameter is 1 cm. System voltage is 66 kV (line value), 3 phase. Determine the maximum stress in the two dielectrics. 5. A 66 kV single cores lead sheathed cable is graded by using two dielectrics of relative permittivity 5 and 3 respectively, thickness of each being 1 cm. The core diameter is 2 cm. Determine the maximum stress in the two dielectrics. 6. Show that in a cable using two intersheaths the maximum stress in the dielectric reduces by the factor 1 / (1/3) (1 + a + a2) of the maximum stress in an ungraded cable where d1 / d = d2 / d1 = D / d2 = a and D = Sheath diameter, d = Core diameter whiled1 and d2 are the diameters of intersheaths. 7. A cable has intersheath grading which satisfies d1 / d = D / d1 = a The conductor diameter is 2 cm while the intersheath diameter is 5 cm. Determine the location of the intersheath. Calculate the ratio cf maximum electric stress with and without intersheath. 8. A single core cable is graded using two dielectrics of relative permittivities 3.6 and 2.5 and thickness of each is 1 cm. The conductor diameter is 1 cm. The system voltage is 66 kV, 3 phase. Determine the peak values cf the maximum stress in the two dielectrics.
Stress in Insulation
Subject and UNIT: Transmission and Distribution: Unit IV: Underground Cables 2. Economical Core Diameter
Questions : 1. Derive an expression for the maximum and minimum dielectric stress in a single core cable and obtain the criterion for keeping the dielctric stress to a minimum value. 2. Derive the expression for the capacitance of a single core cable and give the expression for the maximum and minimum dielectric stress.3. A single core cable has a conductor diameter of a 1 cm and internal sheath diameter of 3 cm. If PVC of relative permittivity 5 is used as the insulation, calculate the capacitance for 1 km length of the cable.4. Prove that the most economical conductor size in a cable is d = D / 2.718 5. Calculate the most economical diameter of a single core cable to be used on 132 kV, 3 phase system. Find also the overall diameter of the insulation if the peak permissible stress is not to exceed 60 kV/cm. 6. Calculate the capacitance and charging current of a single core cable used in 3 phase, 66 kV system. The cable is 1 km long and having a core diameter of 15 cm and impregnated paper insulation of thickness 22.5 cm. The relative permittivity of the insulation may be taken as 3.5 and supply frequency at 50 Hz.