Continuing to build on the success of past industry-open cables workshops in 2008, 2013 and 2014, CEATI International's 2015 event will focus on sharing best practices and emerging issues for safely working on transmission underground cable systems.
Pre-terminated cables such as transformer leads in padmount substations should be tested as per this SWP. They are classed as minor radial cables and do not require a high voltage withstand test. Regarding the use of DC testing such as insulation resistance or leakage measurement during a high voltage DC withstand, there is a phenomenon called electro endosmosis (evident in older insulation rather than XLPE) that causes a lower IR reading (higher leakage current) when the positive terminal is connected to the grounded side of the insulation being tested.
ABSTRACT: Transmission and distribution of power can be done either by overhead lines or power cables. Although for many years, the overhead lines have been most reliable power transmission medium, the deregulation of the electricity supply markets and growing environmental awareness are creating exciting new markets for power transmission solutions based on underground cable technology. Even though many protection methods for high-voltage cable systems this paper deals with the advanced monitoring and detection of voltage stress in MV or HVUndergroundcables. This system is implemented with the help of embedded system in which master slave concept.This paper uses a PIC16F877A micro controller as a master and the sensor network acts as slave. Thus the master and slave communication can be implemented using i2c protocol. In case any abnormal voltage stress across the UG cable, the corrective action has done in both input and output side by using step-down transformer step up transformer. So that balanced output is maintained in the UG cables.
It is well known from the theory and practice that it is very difficult to shield the magnetic field of low frequency. Nevertheless, some simple measures can be applied to avoid the transgression of the afore-mentioned restrictions. One of them is to lead the vertical cables closely (as it is possible) one to each other for the better three-phase compensation of the magnetic field. Another measure is to fence the tower to keep people in an enough distance from the vertical cables. Unfortunately, such a solution is not always possible. The similar solution is to enlarge the vertical cable casing.
Unlike the case for ac cables, there is no physical restriction limiting the distance or power level for HVDC underground or submarine cables. Undergroundcables can be used on shared ROW with other utilities without impacting reliability concerns over use of common corridors. For underground or submarine cable systems there is considerable savings in installed cable costs and cost of losses when using HVDC transmission. The lower cost cable installations made possible by the extruded HVDC cables and prefabricated joints makes long distance underground transmission economically feasible for use in areas with rights-of-way constraints or subject to permitting difficulties or delays with overhead lines.
ABSTRACT:In smart cities, undergroundcables will be used because it has many advantages such as immunity from weather, rainfall, thunderstorm, etc. But it is difficult to detect fault in underground cable. The objective of this project is to detect exact fault location in an underground cable. A set of resistors represents the resistance of cable. When any fault occurs the voltage and current vary which depends on the distance of fault from base substation. The controller will measure and monitor the voltage and current of the cable using analog to digital converter. The exact location of fault will be decided based on changes in voltage and current of cable. This location will be indicated on display. The detection of fault of cable will be simulated using MATLAB software. The identical performance of controller will be represented using PROTEUS software.
Abstract: Overhead transmission lines have been used for decades in the transmission high voltage power from generation point to consumer point. Several factors such as weather condition losses and virtual impacts have led to alternative transmission technology that would address those challenges. Underground power cables are a viable alternative to overhead transmission lines when proper considerations are given to many details of using those types of systems. Cables have different characteristics than overhead lines that must be factored into design, reactive compensation, operation and maintenance and repair. This work provides introduction into cable types and presents overview into consideration for using undergroundcables. Discussion here focusses on transmission cables, but also relevant to distribution cable application
For most of the worldwide operated low voltage, medium voltage and high voltage distribution lines undergroundcables have been used for many decades. To reduce the sensitivity of distribution networks to environmental influences underground high voltage cables are used more and more. They are not influenced by weather conditions, heavy rain, storm, snow and ice as well as pollution. The rising demand for electrical energy increases the importance and priorities of uninterrupted service to customer. Thus, faults in power distribution networks have to be quickly detected, located and repaired.
3.18.5 The following trees and those of similar size, be they deciduous or evergreen, should not be planted within 6.0m of the underground cable circuit: Ash, Beech, Birch, most Conifers, Elm, Horse Chestnut, Lime, Maple, Oak, and Sycamore. Apple and Pear trees also come into this category. These trees may only be planted as individual specimens or a single row in an area between 6.0m and 10.0m of any underground cable circuit. Dense mass planting may only be carried out at distances greater than 10.0m from any underground cable circuit.
An expected, finding from Figure 6.3 reveals many cables in the sub-model will be operating over their 100% rating; these elements are identified by their colour coding and one particular cable WMTS – LS1 will exceed its 140% rating under normal operation condition. Additionally there are more elements identified when n-1 redundancy configuration is used. After identifying all the elements over stressed in this sub-model, single or double circuits are added to keep in line with the Citipower n-1 redundancy configuration. A 22kV XLPE cable with a current rate of 325A which is commonly used by power utilities in Melbourne is employed rather than the 22kV XLPE cable with 280A current rating to enhance the capacity of the feeders and minimise the number of parallel circuits required for normal and contingency operations. Figure 6.5 shows the updated WMTS 22kV underground sub-model where all elements are operating under their 100% rating and n-1 Citipower redundancy configuration is maintained.
One aspect that became evident during this project was that in many areas of the existing network, the model actually de-rated the current capacity of the cables. This led to speculation by the Network Operations Control Centre staff who question the standards and the models by stating that they have been operating the cables well beyond the new ratings for many years with no mishap. This argument was recently unfounded when a cable was dug up and exposed to find that overheating had occurred and the conduit that housed the cable actually deformed dramatically. It is not known as to how much damage the insulation had sustained.
The thermal resistivity and dielectric losses of cable joints are higher than the normal cable because of added insulation. Since the cable joints are mostly hand made, the exact mathematical analysis of the joints is not possible. Direct measurement of temperature rise inside the joint by the method of current injection and thermo couples is not possible for 2?5kv and above rated cables, because of higher dielectric losses.
In this paper IEEE 13 bus radial distribution test feeder is considered for optimum relay coordination between pri- mary and backup directional overcurrent relays. This test feeder offers variety of interesting features. The operating voltage is 4.16 kV. The nodes are separated with moderate distances with adequate load. Thirteen nodes are intercon- nected through ten overhead and two underground line sections which constitutes a combined overhead/cable dis- tribution system. Feeder consists of a voltage regulator, a 115/4.16 kV Δ-Y transformer, 4.16/0.480 kV Y-Y step down transformer is interconnected. Loads are unbalanced with
Second, each cable was connected to a feedthrough and char- acterized at 5 kV for an average of 14 hours (and a minimum time of 3 hours). In order to be accepted for use a cable must have a micro-discharge rate below 10 µd / h and big micro- discharge rate below than 0.1 bµd / h. This limit was set to avoid big rates that could introduce dead time to the experiment or damage the front-end electronics. If they failed the test, the cable and the feedthrough were tested separately to identify which was causing the high micro-discharge rate. Results of the micro-discharge rate per cable are shown in Figure 9 and Table 6. The rate should be considered an upper limit since a contribution to the rate from the feedthrough or other parts of the electronic chain is expected. No issues were found with any of the cables, and a rate less than 5 µd / h was measured for all cables (with ∼ 5% contribution from Bµd’s). The measure- ments were taken in the order displayed in Table 6. The average micro-discharge rate is lower in the last measurements pointing to some micro-discharge events coming from other parts of the system and related to a long-term conditioning rather than only from the cables or feedthroughs. This e ff ect can be observed in Figure 10 where the measurements taken every month have been averaged.
For the static rating a constant current limit is set, where the steady state temperature of the conductor, in the case of over- head lines and cables, and the hotspot temperature in the case of transformers are set to their maximum according to manufac- turers’ datasheets. However, in RTTR, the conductor and hotspot temperature are monitored based on thermal models to decide loading limits. Therefore, in static rating constant loading limits (at least seasonal limits) are used whereas in RTTR time varying loading limits are set. Hence, the overall loading capacity incre- ment, for example, of overhead lines is tightly linked to the ambient temperature, wind speed and solar irradiation. In Finnish weather conditions for a 20 kV bare overhead line, about 58% more deliv- ered energy in one year would be possible in the case of real-time thermal rating rather than static rating. For undergroundcables, however, the time constant is too long to react to instantaneous loading and DG output proﬁle. Hence temporary overloading, espe- cially in the case of contingencies, is viable as long as it is followed by an extended period of low loading. Transformers lie somewhere in between, where whether it is installed inside a room or in the outside environment inﬂuences the real-time thermal rating. In this study, an indoor installation is considered since our test network is for a sub-urban area. Hence, the real-time thermal rating for trans- formers focuses more on overseeing upcoming thermal violations than setting the maximum hourly load limit for the next 24 h.
The Underground XLPE cables are widely used for undergroundcables system especially in urban or compact area that provides many facilities to its community. Although underground XLPE cables possess excellent dielectric strength, low dielectric permittivity, low loss factor, good dimensional stability, solvent resistance and good thermo-mechanical behaviour , unfortunately, there are several weaknesses faced by XLPE cables, which bring down their performance during service. Moisture and water absorptions from environment into cable insulation are some important factors that deteriorate cable performance in service and for worse cases, it would cause the cable system to breakdown [2,7]. From these absorption activities, water treeing phenomena is introduced inside the cable insulation and causing the value of tan delta of power cable insulator to increase [3,6].
Underground XLPE insulator cables are widely used for undergroundcables system especially in urban or compact area that provides many facilities to its community. Although underground XLPE cables possess excellent dielectric strength, low dielectric permittivity, low loss factor, good dimensional stability, solvent resistance and good thermo-mechanical behaviour , unfortunately, there are some weaknesses faced by XLPE cables, which bring down their performance during service. Moisture and water absorptions from environment into cable insulation are some important factors that deteriorates the cable performance in service and for worse cases, it would cause the cable system to breakdown [2,7]. From these absorptions activity, water treeing phenomena is introduced inside the cable insulation and causing the value of tan delta of the cable insulator to increase [3,6].
The overall plan covers the dismantling of approx. 3,200 circuit kilometres of 132 - 150 kV over- head lines and the undergrounding of approx. 2,900 kilometres of new 132 - 150 kV cables. The overhead lines can be dismantled in step with the grid being replaced by cables, but as the plan at the same time involves a restructuring of the transmission grid, the cables-to-overhead lines ratio will not be 1:1. The restructuring is planned to ensure that a balance is struck between the considerations in terms of security of supply, renewable energy expansion, economy, the envi- ronment and the functioning of the electricity market.
An bundle of electrical conductors used for carrying electricity is called as a cable. An underground cable generally has one or more conductors covered with suitable insulation and a protective cover.Commonly used materials for insultion are varnished cambric or impregnated paper.Fault in a cable can be any defect or non- homogeneity that diverts the path of current or affects the performance of the cable.So it is necessary to correct the fault.