Sir Peter Gershon, the Chairman of National Grid, took advantage of a dip in the electricity provider's share price this week as he raised his holding in the company by nearly a half.Gershon, who joined the board back in August 2011, purchased 18,800 shares at 798p a share, costing him a total of £150,024. The transaction, which lifted his stake in the utility firm by 45%, means that he now has a total of 60,286 shares.The move came two weeks after National Grid's full-year results in which it revealed a record operating profit of £3.6m following a "solid operational performance", the company said.After an impressive rise so far this year, high-yielding utility stocks have been under pressure over the past week. While this could simply be a result of profit-taking, some analysts have suggested that the falls could have been in response to the recent rise in government bond yields.Top Director BuysNational Grid (NG.)Director name: Peter GershonAmount purchased: 18,800 @ 798pValue: £150,024Salamander Energy (SMDR) Director name: Mr James MenziesAmount purchased: 30,000 @ 165.50p Value: £49,650Salamander Energy (SMDR) Director name: Mr Michael James PaviaAmount purchased: 10,000 @ 166.10p Value: £16,610