underground main meaning in Hindi

Examples

1. By the mid-1940s, there were of underground mains and serving approximately 1, 650 customers.
2. The engine that would activate the wheel was fueled by steam boilers whose underground mains rushed steam to propel the pistons of its thousand-horsepower engines.
3. Only the facility's underground main phone line was severed, with service to the complex being restored by C & P Telephone within 2?hours after the crash.
4. The 6 underground main generators are also in operation as of May 23, 2012, when the last main generator, No . 27, finished its final test raising capacity to 22.5 GW.