Case study — DC Arc flash and safety considerations in a 400VDC UPS architecture power system equipped with VRLA battery
Case study — DC Arc flash and safety considerations in a 400VDC UPS architecture power system equipped with VRLA battery
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案例研究 — 配备 VRLA 电池的 400VDC UPS 架构电源系统中的直流电弧闪和安全注意事项
DOI：
10.1109/intlec.2014.6972187
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
Michael M. Krzywosz
中科院分区：
文献类型：
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作者：
Michael M. Krzywosz
如今，进入市场的用于数据中心和DC微电网的400 VDC UPS电源系统通常被潜在用户视为依赖于看似高且危险的DC电压，相对于熟悉的电信-48VDC电源系统，或者甚至熟悉的使用208 VAC配电的数据中心AC UPS系统。毕竟，坐在400 VDC公共配电总线上的ICT负载是不熟悉的。用户，而不是电工，必须将端部连接（400 VDC）到设备（服务器），通常通过插头连接到电源板。在当今的400 VDC数据中心UPS电源系统中，已经撰写了解释基本系统安全考虑和技术的论文（即，高电阻中点接地，线路对地电位降至+/-190 VDC，人员/设备故障电流故障保持在5毫安以下）。然而，人们对典型400 VDC总线上的VRLA电池（最常见的UPS备用方法）等储能设备可以提供的直流电弧故障能量的理解有限，也没有太多的主流讨论。众所周知，电池可以提供极高的短路故障电流，但是对于许多潜在的最终用户来说，该信息以及与直流电弧闪光能量计算（以及由此产生的PPE危害风险类别）的关系仍然是一个谜。这是有趣的，因为在今天的传统AC UPS系统中，标称480 VDC电池存在，但由于逆变器而与用户隔离。因此，相同的电弧闪光问题直到逆变器仍然存在，但对于最终客户来说是不熟悉的。在我们的400 VDC UPS中，DC总线一直延伸到终端设备和用户。毕竟，电弧故障（a.k.a.电弧闪光（arc flash）或电弧爆炸（arc blast））的关注仅在过去几年中在ICT装置中的AC世界中成为主流，并且在400 VDC系统中尚未被普遍讨论。今天，电弧闪光将主要是熟悉那些做维护> 208 VAC系统。典型地，在-48VDC电信系统中，相对较少地关注来自电池设备的电弧故障能量，因为从电击危险的角度来看，低电压（<60 V）被视为良性的。闪弧安全性研究很少或从来没有做过这些系统，目前的直流故障研究的回顾表明，工作仍然需要做。此外，直到最近（2012年），国家安全规范甚至才解决了高（> 100 V）直流工作环境，并且通常是从规定的角度来看，而不是理论计算的角度，正如当今行业公认的交流型电弧故障分析中存在的那样。因此，本文将提供一个假设的400 VDC UPS电源系统的照明电弧故障研究。将涵盖以下主题：·描述一个典型的120千瓦系统与VRLA UPS电池。·该典型系统的直流电弧闪光计算，包括多个位置（电池柜、电力系统总线等）的危险分析。·一般讨论事故能源和工人的PPE要求。
Today's 400VDC UPS power systems that are coming to market for data centers and DC micro-grids are often looked at by potential users as relying on a seemingly high and dangerous DC voltage, with respect to familiar telecom -48VDC power systems, or even familiar data center AC UPS systems operating with 208VAC distribution. After all, ICT loads sitting on a 400VDC common distribution bus is unfamiliar. And the user, not electrician, has to make the end connections (400VDC) to the equipment (servers), typically via a plug to the power strip. In today's 400VDC Data center UPS power systems, papers have already been written explaining basic system safety considerations and techniques (i.e., high resistance mid-point grounding, with line to ground potentials lowered to +/-190VDC, and personnel/equipment fault currents faults are kept under 5 milli-amps). However, there's been limited understanding and not much mainstream discussion about DC arc fault energies that can be delivered by energy storage devices such as VRLA batteries (the most common UPS back-up method) on a typical 400VDC bus. It is generally known that batteries can provide extremely high short circuit fault currents, but this information and the relationship to DC arc flash energy calculations (and resultant PPE hazard risk categories) remains a mystery for many potential end users. This is interesting because in today's traditional AC UPS systems, the nominal 480VDC battery exists, but is isolated from the user due to the inverter. Thus, the same issue of arc flash still exists up to the inverter, but is unfamiliar to the end customer. In our 400VDC UPS, the DC bus is extended all the way to the end equipment and user. After all, arc fault (a.k.a. “arc flash” or “arc blast”) concerns have only become mainstream in the AC world in the past several years in ICT installations, and not yet generally discussed in 400VDC systems. Today, arc flash will mostly be familiar with those doing maintenance on >208VAC systems. Typically in -48VDC telecom systems, relatively little concern is shown to arc fault energies from the battery plant, since the low voltage (<;60V) is seen as benign from a shock hazard perspective. Arc flash safety studies are seldom or never done on these systems, and a review of the current research on DC faults shows work still needing to be done. Furthermore, only recently (2012) have national safety specs even addressed high (>100V) DC working environments, and that often from a prescriptive perspective, vs. a theoretical calculation perspective, as exists today in industry accepted AC type arc fault analysis. This paper shall therefore provide an illuminating arc fault study on a hypothetical 400VDC UPS power system. The following topics will be covered: · Description of a typical 120kW system with VRLA UPS batteries. · DC arc flash calculations on this typical system, including analysis of hazards at multiple locations (battery cabinet, power system bus, etc.). · General discussion of incident energy and PPE requirements for workers.