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A Guide to Medium Voltage Cables

Cable basics, Cable selection, Keystone Academy /

  Medium Voltage (MV) are power cables widely used in commercial, industrial, and electrical utility applications. At Keystone, our MV cables have a voltage rating from 6kV to 30kV. In this blog, we will discuss the construction of MV cables and explain how each layer contributes to their overall functionality. Construction of a MV Cable ConductorThere are 2 types of conductors that we use for the construction of our MV cables: Copper and Aluminium. Copper: Made from electrolytic copper with a purity exceeding 99.95%. Aluminium: Drawn from aluminium ingots with a minimum purity of 99.70%. Conductor ScreenOur conductor screen is an extruded cross-linked semi-conducting compound that covers the metallic conductor. This layer acts as a stress point in the insulation, potentially weakening its long-term durability. Insulation ScreenThe insulation screen is a cross-linked semi-conducting compound extruded over the insulation. It provides a smooth surface, serving as a transition material between the insulation where an electric field exists and the conductive metallic screen, where the electric field is zero. Thus, this reduces the stress at the insulation layer. Metallic ScreenThe metallic screen typically consists of a layer of helically applied copper tape with an overlap, over the insulation screen. The metallic screen in a 3-Core cable ensure that the electric field remains contained within the cable core. Cable Assembly (Optional)For 3-Core cables, identification taoes (Brown, Black, Grey) are placed under the metallic screen before the cores are laid up. A non-hygroscopic polypropylene filler is applied between the laid-up cores to provide a circular shape for the overall cable. Polypropylene tape(s) or PETP (Polyester) tape(s) is used as a barrier tape over the laid-up cores. Separation Sheath (Optional)All armoured cables include an extruded layer of Black PVC [1], MDPE [2], or LSZH [3] separation sheath, applied over the core or laid-up cores to prevent corrosion by separating different metals and avoiding galvanic effects. Armour (Optional)In armoured cables, the armour is applied over a separation sheath for additional mechanical protection. Single-core cables use aluminium wires (AWA), double aluminium tape armour (DATA), while multi-core cables use galvanised steel wire armour (SWA), or double galvanised steel tape armour (DSTA). Outer SheathAll cables have an extruded layer of PVC [1], MDPE [2], or LSZH [3] outer sheath over the core, laid-up core, or the armour. This outsheath, usually black, protects the cables from sunlight and termites. Another colour may also be provided upon agreement between the manufacturer and purchaser. [1] Polyvinyl Chloride[2] Medium Density Polyethylene[3] Low Smoke Zero Halogen For more information, check out our Medium Voltage Cables catalogue. Download Catalogue Keystone’s Commitment to Our Clients We are committed to providing exceptional customer satisfaction for our clients through a quality management system. Our experienced and highly skilled inspectors ensure that newly manufactured MV Cables are tested in a clean dust-free room environment and that each cable meets international standards such as IEC 60502-2 and BS 6622. For any enquiries regarding Keystone’s MV Cables, please check in with our sales team. Contact Sales

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Understanding Mechanical Testing for Cable Longevity

Keystone Academy, Quality Assurance /

What is the purpose of mechanical testing? Power cables, typically installed underground, in ducts, or on overhead structures, are often subject to mechanical stresses such as tension, compression, bending, and twisting. Hence it is important that cables are put through stringent tests to ensure they can withstand the mechanical stresses that they will be subjected to during installation, operation, and maintenance. One of the categories we test for in mechanical testing, is the Tensile Elongation test, which affirm that cables manufactured are equipped with mechanical capabilities including flexibility and load-bearing capabilities. By subjecting the cable’s insulation and sheath to tensile elongation test, we can compare it against predetermined minimum elongation and tensile strength based on standards to identify potential weaknesses in the cable’s design or materials to optimise performance. This is fundamental to providing our customers with reliable cables. As cables are meant to operate over a lifespan of 20 to 30 years under normal use conditions, how can we ensure that cables continue to retain mechanical integrity even after long term use? The Tensile Elongation Test We subject our cables to Tensile Elongation to determine whether they can retain tensile strength and elongation after being exposed to a tension load. This assessment determines the cable’s ability to maintain mechanical integrity at ambient temperatures, and is one of the key mechanical tests our cables need to withstand. In this test, a tubular or dumb-bell control sample is prepared and placed in an electromechanical or universal testing machine with 2 clamps and pulled from each end until its breaking point. The test measures the amount of force (N) applied and elongation when the sample breaks (∆L).  Tensile strength – Amount of force (N):  Strength needed to pull the material of the cable until it breaks. The maximum strength it can tolerate Elongation(∆L):  The length that the material of the cable can be stretched until it breaks Subsequently, the control sample is used as a baseline and compared with an aged sample placed in the oven and thereafter subjected to the Tensile Elongation test. Read on to find out more about how we age cable samples. Ageing Conditions Samples To ensure that the cables can maintain mechanical integrity over a 20–30-year lifespan, we subject the materials to accelerated ageing conditions to verify that prolonged use does not negatively affect the cable. It is important to conduct comparison tests with non-aged samples after an accelerated ageing process. To perform the ageing test, the cable is placed in an oven to accelerate the ageing process, simulating decades of usage. This is in line with IEC 60811- 401:2012 standards, which typically applies to crosslinked and thermoplastic compounds used for insulating and sheathing materials in the ageing oven process. The samples placed in the oven are called aged samples. The Importance of Testing  A successful outcome provides assurance that the cables will have a long and reliable service life, which is critical for the safe, efficient operation of electrical power systems, and minimise waste as a result of cable longevity. If a cable is unable to withstand mechanical testing, it can lead to unsafe situations at project sites.  At Keystone Cable, mechanical testing is a standard component of our cable testing regimen. This is our assurance to you that our cables are reliable and adhere to international specifications.   For more information, please reach out to our sales team.

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Selection Guide for the Right Signal Cable

Cable selection, Keystone Academy /

In our previous Keystone Academy blog, “RS485 vs RS422”, we introduced the similarities and differences between the 2 wire protocols, RS485 and RS422. Though similar, the 2 wire protocols are not the same. After knowing their differences, you may be wondering how to select a suitable signal cable. Here, we have distilled the key considerations to look into: Insulation Insulation prevents electrical losses. There are 3 types of plastic insulation, namely Polypropylene (PP), Polyethylene (PE), and Polyvinyl Chloride (PVC). The table below shows a comparison of the 3 materials, although PVC is still the most commonly used.  Screening Screening prevents noise interference such as Electromagnetic Interference (EMI). Data communication cables are usually twisted to screen out noises. In addition to this cable laying method, Keystone adds screen(s) to the cables as a physical measure to further prevent noise interference. There are 2 frequently used screens; the foil screen and the tinned* copper wire braid with foil screen.   Foil screens are used in normal circumstances while tinned copper wire braids with foil screens are used when the environment is extremely noisy. For instance, at industrial plants and factories with many motors running at the background.  *Copper is tinned to provide additional protection against oxidation and corrosion. For more information about other cables with foil screens and cables with tinned copper wire braid with foil screens, check out the details in our Smart City catalogue.

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Oil & Gas: Hazardous Area Classification

Cable basics, Keystone Academy /

The oil and gas industry is hazardous as it is prone to explosions that occur in the presence of 3 substances: flammable gas or dust, oxygen, and an ignition source. Hence, to prevent explosions from occurring, we need to ensure that these 3 substances are not present at the same time. Conversely, as both flammable gas and dust are indispensable in the oil and gas industry, and oxygen is a necessity, the determining factor lies in the prevention of ignition sources. There are different types of hazardous areas and they are classified into zones based on their risk factors. Here we introduce the 3 different zones: Zone 0, Zone 1, and Zone 2. What are the different zones? The hazardous areas are classified into zones based on their likelihood and duration of occurrence of an explosive atmosphere. The zones are:  Zone 0: Explosive gas-air mixture is continously present, or present for long periods. Zone 1: Explosive gas-air mixture is likely to be present in normal operation. Zone 2: Explosive gas-air mixture is not likely to be present, or present for short periods. The different zones require dissimilar protection measures in terms of enclosure type, Zone 0 requires Ex ‘d’ protection, and Zones 1 and 2 requires Ex ‘e’ protection. Our Keystone Oil & Gas cables are structurally designed to fit their respective zones. Keystone Cable’s Oil & Gas Cables Keystone Cable has supplied Oil & Gas cables to iconic projects locally and internationally, such as Tanjong Bin Oil Terminal in Malaysia, Ilijan LNG in the Philippines, Jet Fuel Upgrade @ Yangon Airport in Myanmar, Pluto LNG in Australia, and the Arkema Project @ Jurong Island in Singapore. To find out more about our Oil & Gas cables, contact our Sales team. Contact Sales The oil and gas industry is hazardous as it is prone to explosions that occur in the presence of 3 substances: flammable gas or dust, oxygen, and an ignition source. Hence, to prevent explosions from occurring, we need to ensure that these 3 substances are not present at the same time. Conversely, as both flammable gas and dust are indispensable in the oile and gas industry, and oxygen is a necessity, the determining factor lies in the preventation of ignition sources. There are different types of hazarous areas and they are classified into zones based on their risk factors. Here we introduce the 3 different zones: Zone 0, Zone 1, and Zone 2. What are the different zones?   The hazardous areas are classified into zones based on their likelihood and duration of occurrence of an explosive atmosphere. The zones are: Zone 0: Explosive gas-air mixture is continously present, or present for long periods. Zone 1: Explosive gas-air mixture is likely to be present in normal operation. Zone 2: Explosive gas-air mixture is not likely to be present, or present for short periods. The different zones require dissimilar protection measures in terms of enclosure type, Zone 0 requires Ex ‘d’ protection, and Zones 1 and 2 requires Ex ‘e’ protection. Our Keystone Oil & Gas cables are structurally designed to fit their respective zones. Zone 0: Explosivie gas-mixture is continously present, or present for long periods. Zone 1: Explosive gas-mixture is likely to be present in normal operation. Zone 2: Explosive gas-air mixture is not likely to be present, or present for short periods. The different zones require dissimilar protection measures in terms of enclosure type, Zone 0 requires Ex ‘d’ protection, and Zones 1 and 2 requires Ex ‘e’ protection. Our Keystone Oil & Gas cables are structurally designed to fit their respective zones. Keystone’s Oil & Gas Cables Keystone Cable has supplied Oil & Gas cables to iconic projects locally and internationally, such as Tanjong Bin Oil Terminal (Malaysia), Ilijan LNG (the Philippines), Jet Fuel Upgrade @ Yangon Airport (Myanmar), Pluto LNG (Australia), and the Arkema Project @ Jurong Island (Singapore). To find out more about our Oil & Gas cables, contact our Sales team. Contact Sales

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RS485 vs RS422 Similarities and Differences

Cable basics, Keystone Academy /

In data communication, there are low-frequency and high-frequency communication. For low-frequency data communication, 2 wire protocols are commonly used: RS422 and RS485. Wire protocols are guidelines for the transmission of data from point to point. Both of these “RS” protocols, RS422 and RS485, are also known as TIA-422-B, and TIA-485-A respectively. Cables following these protocols are robust and can transmit data to long distances and in noisy environment. However, as the distance increases, the speed of data transmission decreases. The distance can be calculated using the Baud Rate chart and the frequency of data transmission can be adjusted accordingly.  These low-frequency cables are generally used in sensors and devices that do not require high data speed. How are these protocols, RS422 and RS485, similar or different? Similarities Protocols RS422 and RS485 are similar in many ways. Some of their similarities are: 1. Both use differential signaling over twisted pairs. 2. Both can be made into full-duplex using 4 wires. 3. Both can transmit data up to 1.2km, at a rate of up to 10Mbps. Differences Though similar, the 2 protocols are not the same. RS485 is more advanced than RS422. RS485 is backward compatible while RS422 is not. In other words, systems following RS485 are RS422 compatible but systems following RS422 are not RS485 compatible. RS485 is convenient for multi-point interconnection and can be networked to form a distribution system that allows up to 32 drivers and 256 receivers. RS422, on the other hand, allows 1 driver and 10 receivers. Keystone Cable’s Signal Cables At Keystone, we supply cables such as UL2464 Single Pair Signal cables, UL2464 Multi Pair – OS Signal cables, and RS485 Multi Pair Double Overall Screened cables (sample construction below). These cables can be used for both RS422 and RS485.  RS485 Cable Construction Download Catalogue Download our Smart City catalogue to view the Keystone Signal Cables offered. For more enquiries, please contact us. Contact Sales

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Understanding Variable Speed Drive Cables

Cable basics, Cable selection, Keystone Academy /

Power and control cables transmit and distribute electrical energy in various applications. In cases where Electromagnetic Compatibility (EMC) is required, Variable Speed Drive (VSD) cables become an attractive choice. What are VSD Cables? VSD cables are 3-core cables specially designed to limit the effects of Electromagnetic Interference (EMI). They are screened, heavy-duty cables for machinery that requires speed control.  They are used in control and motor systems supply in industrial water pumps, conveyor systems, textile machines, cranes, and paper industries. Symmetrical Design VSD cables are designed symmetrically, where 3 earth conductors are situated in the interstices of the 3 phase conductors. This enables us to achieve a minimal ground current, reducing the chances of bearing fluting and thus preventing motor bearing failure. Keystone Cable’s VSD Cables Our VSD cables have been selected for iconic projects in Singapore and Australia, such as the Jurong Island Desalination Plant in Singapore, Amazon Data Centre in Singapore, and overseas, such as BHP Billiton – Macedon in Australia. We have a strong cable specialist technical team to provide recommendations for your projects. Please contact us should you require more information. Contact Sales

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SS 299:2021 Updates – Fire Resistant Test Standard

Cable basics, Keystone Academy, Quality Assurance /

In our previous Keystone Academy blog, ‘Fire resistant test standards-explained!‘. we introduced the differences among the 3 common LSZH FR test standards. In Singapore, Fire-resistant (FR) cables undergo tests given by the Singapore standard, SS 299. SS 299:2021 standards specifies the requirements of FR cables relating to characteristics required to maintain circuit integrity and the ability to reduce flame spread, emit low levels of smoke, and emit halogen-free gas during a fire. This is essential as it ensures that the power supply can be sustained so that life-saving electrical installations, such as fire alarms, smoke detectors, PA systems, and emergency lighting, can perform their functions even in the event of a fire. According to the updated Singapore FR Test standard (SS 299:2021), passing Protocols C, W, and Z is mandatory for FR cables to be fully compliant. Additionally, including other protocols, namely Protocols A, B, S, X, and Y from previous editions, is considered obsolete. This revised version was published on 23 September 2021. Fire-resistant tests: SS 299:2021 (from 23 September 2021 onwards) Fire-resistant tests: SS 299-1:1998 (before 2021) Resistant to fire alone (Category A, B, C, or S)OPTIONAL: Resistance to fire with water (Category W)This is meant to simulate fire in the presence of activated sprinkler systems. OPTIONAL: Resistance to fire with mechanical shock (Category X, Y, or Z)This is meant to simulate fire in the presence of disturbances such as falling debris. Check in with our sales team to learn more about how we can help you maintain circuit integrity while delivering energy or if you need further guidance on how the new regulation impacts your business. Contact Sales

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What are the different classes of cable conductors?

Cable basics, Keystone Academy /

A cable conductor is the primary component of electrical cables. It refers to the metallic wire or wires that carry the electrical signal through the cable. Here, we examine the four different Copper (Cu) conductor categories: Class 1, Class 2, Class 5, and Class 6. Why are there different categories? The Cu conductors are grouped according to their flexibility; the higher the class, the more flexible it is. The flexibility of the Cu conductor of a cable will differ based on its unique purpose of use. The simplest conductor is a single, solid wire (Class 1). Although it offers a smaller cable in terms of diameter, the largest Cross-Sectional Area (CSA), and the purest signal, it is mechanically weak and is prone to breakage after a few cycles of bending. To improve flexibility, wires are stranded together. The more wires that are stranded together to make a given size, the more flexible the conductor will be. This implies that the higher the class, the more strands in the conductor. Furthermore, when wires are stranded together, they are much easier to bend and move during installation than a single wire with the same cross-section. Those in classes 1 and 2 are intended for use in cables for fixed installations. On the other hand, those in classes 5 and 6 are designed for use in flexible cables and cords but may also be used for fixed installations. The table below compares the different Cu conductors’ different categories. Contact us if you would like to find out more about the cable types to choose for your cabling requirement.

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