情况
来自俄克拉荷马州塔尔萨的埃文斯企业的Tim Deschamp正在与客户合作，以帮助他们解决并减少炉子控制室中电气危害的关键问题。较早的Arc-Flash分析确定，从3500 kVA变压器馈送的一个480伏柜超过了Arc-Flash危险风险类别4（HRC）。这意味着如果工人开放，则不允许工人接近内阁。因此，机柜的门保持关闭，与它有关的一切都远程完成。问题在于，内阁以及相关的变压器可供员工访问。这显然是一个不可接受且不安全的情况。
"Had this relay not been there, they were looking at between $800,000 to $1 million of cost..."
Deschamp knew that to be able to work on the cabinet or lower required PPE, he needed to find a way to lower the HRC. He selected the PGR-8800 Arc-Flash Relay from Littelfuse, which could be easily retrofitted in to the existing cabinet. This device can lower incident energy by detecting a developing arc flash and sending a trip signal to the breaker within 1 ms. Deschamp was wary of durability and maintenance problems that he had experienced with other relay manufacturers and wanted a solution that would be both reliable and easy to maintain.
Deschamp installed the Littelfuse PGR-8800 Arc-Flash Relay in the controls section of the cabinet, with two light sensors mounted in each of the three power compartments. The trip output of the relay was connected to the shunt trip input of the main breaker.
Trial by Fire
这个装置的时机非常幸运。多年来，制造过程中使用的沙子在柜子下方的电缆周围积聚。因此，电缆绝缘材料因此变得脆弱。发生某事发生只是时间问题，在安装PGR-8800后仅一周，该工厂经历了Arc-Flash事件。如果不在PGR-8800中继，此事件将对设施和停机时间造成灾难性损害。这一切都是从机柜下方的一条电缆中的相处断层开始的。弧线将电缆追踪到机柜内部的主要公共汽车，在那里它威胁要升级为三相断层，吸收更多的能量并可能破坏机柜，甚至可能会破坏植物，更不用说对任何一项效果通常在附近的人。
当弧线到达机柜时，所有六个光传感器都对明亮的弧形闪光反应，甚至没有直接视线的光线。ARC-FLASH继电器立即响应，在不到1 ms的情况下向主断路器发送了旅行信号。Deschamp能够确认这一点，因为每个传感器都显示其行程状态。没有PGR-8800，主断路器的反应就不会足够快，无法阻止灾难性的弧形闪光灯。取而代之的是，损坏是最小的：将一块拇指大小的金属从其中一条公共汽车杆上燃烧。机柜和内部的开关设备仅遭受轻微破坏。
节省100万美元
“Had this relay not been there, they were looking at between $800,000 and $1 million of cost, considering downtime and equipment replacement,” Deschamp said. “Besides the lead-time for delivery and the installation, they would have had to cut a hole in the outside wall of the plant to install it.” Deschamp estimates that lead-time on electrical equipment of that size, with 4000-amp capacity, would be anywhere from 10 to 24 weeks— and that’s just for delivery, not installation.
"It was a very easy installation compared to most relays"
The actual cost of the replacement switchgear would have been a small portion of the overall loss for the plant. Instead, the entire cost to the end-user was only $6000, which included replacing a few insulators and a portion of the bus bar. Fortunately Evans Enterprises, Tulsa, Oklahoma, was able to obtain the 1970s-vintage equipment and the plant was back up and running within 24 hours. Immediately after the incident, the customer requested that Deschamp install Littelfuse PGR-8800 Arc-Flash relays in all of their larger electrical cabinets.
概括
This is an example of how a minimal investment of just a few thousand dollars can save tremendous costs in lost equipment, downtime and production, not to mention the risk of employee injury or fatality. This customer was fortunate with his timing, but a proactive strategy is recommended when it comes to protecting critical assets and employee safety. An arc-flash relay is an integral component of an arc-flash protection scheme that can minimize damage and save money, time, and lives. For more information on the PGR-8800 Arc-Flash Relay, visitlittelfuse.com/arcflash
